Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Mon Jun 07 2010, 01:41AMSo i decided not to quit on my ray machine.
Any input? Please have some input.
Re: Grenadier's big thread of Röntgen related shenanigans
Wolfram, Mon Jun 07 2010, 10:24AM
Was the head an S.S. White?
I'm almost certain the transformer is a 60Hz unit with a 110V primary, the reason you got such a high voltage from it when giving it 12V on the primary is that when the voltage on the primary was removed, the magnetic field in the core collapsed and induced a high voltage in both the primary and the secondary. If you had connected an oscilloscope across the primary when doing the test, I bet you would see spikes of a couple of hundred volts.
The way you are driving the transformer with a pulsed relay is not right, it will give you some high voltage, but at very limited power, and you might excite resonances in the transformer secondaries, giving you a much higher output voltage than expected, risking the transformer and making the output voltage hard to predict. The transformer is made to be driven by a 60Hz sine wave, and this is certainly the best way to do it.
The transformer has two secondaries that are wound in the opposite direction, and there should be a black wire from the inner end of each secondary. These two wires should be connected to each other and to the core at all times when you are operating the transformer, or else there is a very real risk of arc-over between the inner windings of the secondaries and the core. If you want to measure the current through the transformer (which is also the current flowing through the x-ray tube), you can connect an AC milliampere meter in series with one of these wires.
Here
is the schematic of a typical x-ray head, I hope this clears up any confusion
The transformer should be immersed in oil unless you are operating it at very low output voltages, I wouldn't risk running it at more than 10kVp per secondary without oil. You might be able to operate the tube at 60kVp in air before you start to get trouble with corona and arcing, but I'm a bit worried about the wooden support you're using for the tube. Wood isn't a very good insulator unless it has been thoroughly dried and laquered. Also, running the tube out of oil will limit the maximum power that you can put into it.
Doing these changes will greatly increase the the maximum radiation output of your setup. It will also increase the controllability of the system, both in the sense that you can predictably set the working voltage by giving the transformer a specific AC voltage on the input (a variac will be handy here) and in the sense that you can see what current it is running at. And if you want to run it at low power, that's no problem, just run the tube at a very low current.
Was there a ceramic radiation-shielding tube around the x-ray tube when you removed it from the head? It could be a good idea to put this back on the tube, to shield against off-axis radiation.
I should add the obligatory warning about ionizing radiation, but you seem to know what you're doing safery-wise, the lead shileding box that you've built is a very good protective measure, just don't assume that it will stop all radiation at all times. Normal geiger counters aren't the most suitable for measuring X-rays, but Proud Mary knows much more on this subject than me, and hopefully she can give you some tips.
Anders M.
Wolfram, Mon Jun 07 2010, 10:24AM
Was the head an S.S. White?
I'm almost certain the transformer is a 60Hz unit with a 110V primary, the reason you got such a high voltage from it when giving it 12V on the primary is that when the voltage on the primary was removed, the magnetic field in the core collapsed and induced a high voltage in both the primary and the secondary. If you had connected an oscilloscope across the primary when doing the test, I bet you would see spikes of a couple of hundred volts.
The way you are driving the transformer with a pulsed relay is not right, it will give you some high voltage, but at very limited power, and you might excite resonances in the transformer secondaries, giving you a much higher output voltage than expected, risking the transformer and making the output voltage hard to predict. The transformer is made to be driven by a 60Hz sine wave, and this is certainly the best way to do it.
The transformer has two secondaries that are wound in the opposite direction, and there should be a black wire from the inner end of each secondary. These two wires should be connected to each other and to the core at all times when you are operating the transformer, or else there is a very real risk of arc-over between the inner windings of the secondaries and the core. If you want to measure the current through the transformer (which is also the current flowing through the x-ray tube), you can connect an AC milliampere meter in series with one of these wires.
Here
is the schematic of a typical x-ray head, I hope this clears up any confusionThe transformer should be immersed in oil unless you are operating it at very low output voltages, I wouldn't risk running it at more than 10kVp per secondary without oil. You might be able to operate the tube at 60kVp in air before you start to get trouble with corona and arcing, but I'm a bit worried about the wooden support you're using for the tube. Wood isn't a very good insulator unless it has been thoroughly dried and laquered. Also, running the tube out of oil will limit the maximum power that you can put into it.
Doing these changes will greatly increase the the maximum radiation output of your setup. It will also increase the controllability of the system, both in the sense that you can predictably set the working voltage by giving the transformer a specific AC voltage on the input (a variac will be handy here) and in the sense that you can see what current it is running at. And if you want to run it at low power, that's no problem, just run the tube at a very low current.
Was there a ceramic radiation-shielding tube around the x-ray tube when you removed it from the head? It could be a good idea to put this back on the tube, to shield against off-axis radiation.
I should add the obligatory warning about ionizing radiation, but you seem to know what you're doing safery-wise, the lead shileding box that you've built is a very good protective measure, just don't assume that it will stop all radiation at all times. Normal geiger counters aren't the most suitable for measuring X-rays, but Proud Mary knows much more on this subject than me, and hopefully she can give you some tips.
Anders M.
Re: Grenadier's big thread of Röntgen related shenanigans
Steve Conner, Mon Jun 07 2010, 10:51AM
I'm puzzled. Why would you take apart a working X-ray head and use the tube and transformer to build another X-ray head?
Are you doing fine art radiography, so you had to take the shielding off to let the low-energy rays out? But then, why not just take the aluminium filter off the original head?
I agree by the way, the lead shielding box is pretty cool.
Steve Conner, Mon Jun 07 2010, 10:51AM
I'm puzzled. Why would you take apart a working X-ray head and use the tube and transformer to build another X-ray head?
Are you doing fine art radiography, so you had to take the shielding off to let the low-energy rays out? But then, why not just take the aluminium filter off the original head?
I agree by the way, the lead shielding box is pretty cool.
Re: Grenadier's big thread of Röntgen related shenanigans
Proud Mary, Mon Jun 07 2010, 01:22PM
Thanks for the plug, Anders, but if you look at my Geigermania thread in the Projects section, you'll see that I'm only at the very beginning of any real understanding of gas amplification detectors, but I will say that GM tubes are wholly unsuitable for the measurement of X-rays, and nowhere worse than around 60-75keV, where the uncompensated energy response curves of typical tubes looks much like Mount Fuji.
Without measurement you have no science.
Proud Mary, Mon Jun 07 2010, 01:22PM
Anders M. wrote ...
Normal geiger counters aren't the most suitable for measuring X-rays, but Proud Mary knows much more on this subject than me, and hopefully she can give you some tips.
Normal geiger counters aren't the most suitable for measuring X-rays, but Proud Mary knows much more on this subject than me, and hopefully she can give you some tips.
Thanks for the plug, Anders, but if you look at my Geigermania thread in the Projects section, you'll see that I'm only at the very beginning of any real understanding of gas amplification detectors, but I will say that GM tubes are wholly unsuitable for the measurement of X-rays, and nowhere worse than around 60-75keV, where the uncompensated energy response curves of typical tubes looks much like Mount Fuji.
Without measurement you have no science.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Mon Jun 07 2010, 06:42PM
Well, of course the tube and transformer are immersed in cooking oil. I've had very good luck with canola oil. I've pushed that transformer to 200KV and it holds up fine. Canola oil has a D-strength of 12MV/M.
The wood is just to hold the tube. It's soaked through in oil.
The transformer is rigged to have the center tap grounded to the core.
I don't plan on any fine measurement with my GM tube, But it is a mica window model (tube, not pancake), and thus very sensitive to all kinds of radiation. It is mainly just going to be used to detect any changes over background.
IF YOU LOOKED AT PAGE 2 OF THE THREAD... you will see that i have a new circuit to drive it. Here is the diagram..
Adam Munich, Mon Jun 07 2010, 06:42PM
Well, of course the tube and transformer are immersed in cooking oil. I've had very good luck with canola oil. I've pushed that transformer to 200KV and it holds up fine. Canola oil has a D-strength of 12MV/M.
The wood is just to hold the tube. It's soaked through in oil.
The transformer is rigged to have the center tap grounded to the core.
I don't plan on any fine measurement with my GM tube, But it is a mica window model (tube, not pancake), and thus very sensitive to all kinds of radiation. It is mainly just going to be used to detect any changes over background.
IF YOU LOOKED AT PAGE 2 OF THE THREAD... you will see that i have a new circuit to drive it. Here is the diagram..
Re: Grenadier's big thread of Röntgen related shenanigans
Wolfram, Mon Jun 07 2010, 09:52PM
That looks like a much more reasonable circuit.
I last checked that thread right after you first joined here, so I missed the updates. No need to yell.
Are you sure about the 200kV figure? How did you measure this? Resistive dividers can be inaccurate even at 60Hz if they have significant stray capacitances, and the 1kV/mm formula for sparks between needle points can overestimate the voltage when yo go above a few tens of kilovolts. You mention the transformer is a 75kV unit, and I'd bet the core saturates at less than 90kV out.
Looking at the picture of the transformer again, I see that I misunderstood at first, the two black wires are of course the primary. The silver colored braided wire from one of the secondaries is the current measurement point, so if you connect a say 100 ohm resistor between this point and and the core, you can measure the current going through the tube, 100mV/mA obviously.
Also, once you have got it working properly, I would either just remove the bulb or at least connect a wire back to the control box from the point between the bulb and the transformer. You want to know the primary voltage, because that tells you the approximate secondary voltage. And you need to know the tube voltage to get consistent exposures.
Anders M.
Wolfram, Mon Jun 07 2010, 09:52PM
That looks like a much more reasonable circuit.
I last checked that thread right after you first joined here, so I missed the updates. No need to yell.
Are you sure about the 200kV figure? How did you measure this? Resistive dividers can be inaccurate even at 60Hz if they have significant stray capacitances, and the 1kV/mm formula for sparks between needle points can overestimate the voltage when yo go above a few tens of kilovolts. You mention the transformer is a 75kV unit, and I'd bet the core saturates at less than 90kV out.
Looking at the picture of the transformer again, I see that I misunderstood at first, the two black wires are of course the primary. The silver colored braided wire from one of the secondaries is the current measurement point, so if you connect a say 100 ohm resistor between this point and and the core, you can measure the current going through the tube, 100mV/mA obviously.
Also, once you have got it working properly, I would either just remove the bulb or at least connect a wire back to the control box from the point between the bulb and the transformer. You want to know the primary voltage, because that tells you the approximate secondary voltage. And you need to know the tube voltage to get consistent exposures.
Anders M.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Mon Jun 07 2010, 10:07PM
Nah, if i run it like an induction coil i can get a 6" spark out of it. I'd say that's at least 200kv.
If I remove the bulb, i get way too much current flowing through the thing. It'll draw about 12A unballasted.
I'll definitely use the current measurement point now.
Since it is a 3 wire cord I'm using, I'll feed a line after the bulb through the ground wire. to measure it at the control box. (obviously I'm not plugging this cord into the mains)
Another problem i have is, the transformer has a 500ms voltage spike while the light bulb warms up and builds it's resistance. I was thinking of just turning the heater on a second late, but that HV needs to go somewhere... Any better ballast ideas than a 60w light bulb?
I could possibly keep the bulb warm and switch via relay to the transformer, however my extension cord has only 3 wires. I won't be able to measure the voltage and keep the bulb warm. I could put the ssr on the machine itself, but i don't want that failing in case a stray x-ray hits it.
Oh and yeah, it was an ss.white rebranded keystone
Adam Munich, Mon Jun 07 2010, 10:07PM
Nah, if i run it like an induction coil i can get a 6" spark out of it. I'd say that's at least 200kv.
If I remove the bulb, i get way too much current flowing through the thing. It'll draw about 12A unballasted.
I'll definitely use the current measurement point now.
Since it is a 3 wire cord I'm using, I'll feed a line after the bulb through the ground wire. to measure it at the control box. (obviously I'm not plugging this cord into the mains)
Another problem i have is, the transformer has a 500ms voltage spike while the light bulb warms up and builds it's resistance. I was thinking of just turning the heater on a second late, but that HV needs to go somewhere... Any better ballast ideas than a 60w light bulb?
I could possibly keep the bulb warm and switch via relay to the transformer, however my extension cord has only 3 wires. I won't be able to measure the voltage and keep the bulb warm. I could put the ssr on the machine itself, but i don't want that failing in case a stray x-ray hits it.
Oh and yeah, it was an ss.white rebranded keystone
Re: Grenadier's big thread of Röntgen related shenanigans
Wolfram, Mon Jun 07 2010, 10:35PM
I would use a wirewound resistor instead of the bulb, a 100W or 200W one would be fine, though I'm still not convinced it's really neccesary. If the transformer draws a lot of current that's either saturation, which should only happen at close to full input voltage, or too high voltage on the filament of the x-ray tube which leads to it drawing more current than it should, and therefore also the transformer also drawing more current from mains. In the first case, just turn the variac back a little bit, and the no-load current should go down to almost zero, and in the latter case reduce the filament voltage. If you measured 12A with the transformer connected directly to mains without the variac and the secondary unloaded, it was also because of saturation. This is a picture I found that illustrates saturation, but the numbers on the scale could be different in your case. These X-ray transformers are also often made to be run at reduced mains voltage from the control unit which explains why it would saturate when connected directly to mains. Do a quick test with the variac to see at which input voltage the primary current starts to get uncomfortable at.
A 6'' spark does not automatically indicate 200kV. See the pictures almost at the bottom of this page for a 160kV X-ray supply making 12'' arcs.
Are you planning on using intensifying cassettes?
Anders M.
Wolfram, Mon Jun 07 2010, 10:35PM
I would use a wirewound resistor instead of the bulb, a 100W or 200W one would be fine, though I'm still not convinced it's really neccesary. If the transformer draws a lot of current that's either saturation, which should only happen at close to full input voltage, or too high voltage on the filament of the x-ray tube which leads to it drawing more current than it should, and therefore also the transformer also drawing more current from mains. In the first case, just turn the variac back a little bit, and the no-load current should go down to almost zero, and in the latter case reduce the filament voltage. If you measured 12A with the transformer connected directly to mains without the variac and the secondary unloaded, it was also because of saturation. This
is a picture I found that illustrates saturation, but the numbers on the scale could be different in your case. These X-ray transformers are also often made to be run at reduced mains voltage from the control unit which explains why it would saturate when connected directly to mains. Do a quick test with the variac to see at which input voltage the primary current starts to get uncomfortable at. A 6'' spark does not automatically indicate 200kV. See the pictures almost at the bottom of this
page for a 160kV X-ray supply making 12'' arcs.Are you planning on using intensifying cassettes?
Anders M.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Mon Jun 07 2010, 10:56PM
I still want a ballast, because I'd rather have a long exposure with a moderate amount of activity than a short exposure with alot of activity [more dangerous]. Plus, i don't want to accidentally blow up my tube.
With a 60w bulb and the thin sparks able to connect at Just over 6cm {wire electrodes, no balls} the transformer draws .3A, with 50V across the primary. There are no arcs formed, just sparks. This leads me to believe that the output is in the sub-ma range, which is what I'm looking for.
A cold 60w bulb has a resistance of 16 ohms, hot 240 ohms. I'd like the kvp to be higher, because even if the transformer is the 90kv model [wasn't labeled], 50v on the primary only means about 45kv on the secondary, which makes sense with the 6.2cm sparks on braided wire electrodes. That's a little low. I'd like up to 65kVp. (75 can't be achieved, because ballasting also lowers the voltage. Should've bought the 0-140V variac.) Anyone know where to find a cheap 0-250ohm 50w rheostat? I can't afford to pay $30 for one...
Also, the ballasted transformer draws .5A when the sparks can't connect.
I also really need a better way of measuring kV.
The tube isn't connected yet, because my 0-120v variac is still in the mail. I want to figure out the circuitry before i put in the tube.
Yes, i am going to use intensifying cassettes and kodak b/w paper film.
Adam Munich, Mon Jun 07 2010, 10:56PM
I still want a ballast, because I'd rather have a long exposure with a moderate amount of activity than a short exposure with alot of activity [more dangerous]. Plus, i don't want to accidentally blow up my tube.
With a 60w bulb and the thin sparks able to connect at Just over 6cm {wire electrodes, no balls} the transformer draws .3A, with 50V across the primary. There are no arcs formed, just sparks. This leads me to believe that the output is in the sub-ma range, which is what I'm looking for.
A cold 60w bulb has a resistance of 16 ohms, hot 240 ohms. I'd like the kvp to be higher, because even if the transformer is the 90kv model [wasn't labeled], 50v on the primary only means about 45kv on the secondary, which makes sense with the 6.2cm sparks on braided wire electrodes. That's a little low. I'd like up to 65kVp. (75 can't be achieved, because ballasting also lowers the voltage. Should've bought the 0-140V variac.) Anyone know where to find a cheap 0-250ohm 50w rheostat? I can't afford to pay $30 for one...
Also, the ballasted transformer draws .5A when the sparks can't connect.
I also really need a better way of measuring kV.
The tube isn't connected yet, because my 0-120v variac is still in the mail. I want to figure out the circuitry before i put in the tube.
Yes, i am going to use intensifying cassettes and kodak b/w paper film.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Mon Jun 07 2010, 11:31PM
just tried a 100w bulb as the ballast, i get .5a draw, 11cm sparks on wire [80% humidity], 100v across the primary with loud skinny sparks (no arcs).
So... this should be 50 watts drawn by the transformer, and at .6mA maximum @75kV. Perfect!
With the variac, i can lower the input voltage, thus lowering the output. Not quite sure if it will lower mA. At a lower voltage, it could possibly draw more amps to keep the 50W draw.
edit:
hmm, it draws .8A with the secondary shorted. So .8ma is still acceptable.
edit2:
So, i tried it with an equivalent resistor. Being a fixed load, it allowed the transformer to draw 2.8A when the wires were close. not good. So i will have to use a lightbulb. However, i need to keep the bulb warm, otherwise i get a voltage spike during warm-up. I can't just leave the heater off, because that spike needs to go somewhere, so i will ditch thte ssr, and use a spdt relay. The relay when de-energized will keep the bulb warm, it'll then energize and switch the bulb through the transformer. Instead of a high voltage going low [bulb warms] i'll have a low voltage going high [bulb cools].
Bad drawing.
Mod edit: Oversized picture. You also win the OMG Worst Schematic Evur award.
Adam Munich, Mon Jun 07 2010, 11:31PM
just tried a 100w bulb as the ballast, i get .5a draw, 11cm sparks on wire [80% humidity], 100v across the primary with loud skinny sparks (no arcs).
So... this should be 50 watts drawn by the transformer, and at .6mA maximum @75kV. Perfect!
With the variac, i can lower the input voltage, thus lowering the output. Not quite sure if it will lower mA. At a lower voltage, it could possibly draw more amps to keep the 50W draw.
edit:
hmm, it draws .8A with the secondary shorted. So .8ma is still acceptable.
edit2:
So, i tried it with an equivalent resistor. Being a fixed load, it allowed the transformer to draw 2.8A when the wires were close. not good. So i will have to use a lightbulb. However, i need to keep the bulb warm, otherwise i get a voltage spike during warm-up. I can't just leave the heater off, because that spike needs to go somewhere, so i will ditch thte ssr, and use a spdt relay. The relay when de-energized will keep the bulb warm, it'll then energize and switch the bulb through the transformer. Instead of a high voltage going low [bulb warms] i'll have a low voltage going high [bulb cools].
Bad drawing.
Mod edit: Oversized picture. You also win the OMG Worst Schematic Evur award.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Tue Jun 08 2010, 11:20PM
Here's the new schematic. (i forgot to put in the second reed relay but you get the picture). It should keep the bulb warm, and there will be no voltage spike.
As for a lead apron, i'm going to make one out of lead flashing and a cooking apron. Even though it's not necessary, as i'll be 250-400' away and the rays will be in the 4mm lead box; i'd feel safer in one. Mainly i won't need more than 45kVp though.
Too bad i can't use a resistor. That would've been easier. However, the light bub becomes more resistive as the transformer tries to draw more current, where as a power resistor does not. I'll start with a 60w lightbub, and if that's not enough i'll go to 75, then 100. Still, any better way?
BTW; does anyone have a schematic for an ss-white marksman?
Adam Munich, Tue Jun 08 2010, 11:20PM
Here's the new schematic. (i forgot to put in the second reed relay but you get the picture). It should keep the bulb warm, and there will be no voltage spike.
As for a lead apron, i'm going to make one out of lead flashing and a cooking apron. Even though it's not necessary, as i'll be 250-400' away and the rays will be in the 4mm lead box; i'd feel safer in one. Mainly i won't need more than 45kVp though.
Too bad i can't use a resistor. That would've been easier. However, the light bub becomes more resistive as the transformer tries to draw more current, where as a power resistor does not. I'll start with a 60w lightbub, and if that's not enough i'll go to 75, then 100. Still, any better way?
BTW; does anyone have a schematic for an ss-white marksman?
Re: Grenadier's big thread of Röntgen related shenanigans
Wolfram, Wed Jun 09 2010, 08:44AM
One possible caveat that I see is that the relay needs to stand off half of the maximum tube voltage between the coil part and the switch part. The battery and filament current rheostat will also be floating at this voltage. DO NOT consider grounding the cathode of the tube unless you've connected it to the center tap of the transformer. If you ground the output of one side of the transformer, the core will float at half of the tube voltage, and the insulation between the core and primary will break down. It is a good idea to ground the core of the transformer in any case.
Do you want a schematic of the control unit or of the x-ray head? If it's the latter, the schematic I posted earlier is going to be quite close.
Anders M.
Wolfram, Wed Jun 09 2010, 08:44AM
One possible caveat that I see is that the relay needs to stand off half of the maximum tube voltage between the coil part and the switch part. The battery and filament current rheostat will also be floating at this voltage. DO NOT consider grounding the cathode of the tube unless you've connected it to the center tap of the transformer. If you ground the output of one side of the transformer, the core will float at half of the tube voltage, and the insulation between the core and primary will break down. It is a good idea to ground the core of the transformer in any case.
Do you want a schematic of the control unit or of the x-ray head? If it's the latter, the schematic I posted earlier is going to be quite close.
Anders M.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Wed Jun 09 2010, 10:46AM
No, i planned to leave the tube floating, the transformer grounded to the big lead box grounded to a water pipe or something. When adjusting the filament voltage, the mains switch will be disengaged. The relay isn't going to be useless, because it is only switching a net voltage of 3.7V. However i'm worried about backflow into the arduino though, which is why i have one relay controlling another. besides, if anything goes wrong i can always kill the mains.
And yes, control unit if you have it.
Adam Munich, Wed Jun 09 2010, 10:46AM
Anders M. wrote ...
One possible caveat that I see is that the relay needs to stand off half of the maximum tube voltage between the coil part and the switch part. The battery and filament current rheostat will also be floating at this voltage. DO NOT consider grounding the cathode of the tube unless you've connected it to the center tap of the transformer. If you ground the output of one side of the transformer, the core will float at half of the tube voltage, and the insulation between the core and primary will break down. It is a good idea to ground the core of the transformer in any case.
Do you want a schematic of the control unit or of the x-ray head? If it's the latter, the schematic I posted earlier is going to be quite close.
Anders M.
One possible caveat that I see is that the relay needs to stand off half of the maximum tube voltage between the coil part and the switch part. The battery and filament current rheostat will also be floating at this voltage. DO NOT consider grounding the cathode of the tube unless you've connected it to the center tap of the transformer. If you ground the output of one side of the transformer, the core will float at half of the tube voltage, and the insulation between the core and primary will break down. It is a good idea to ground the core of the transformer in any case.
Do you want a schematic of the control unit or of the x-ray head? If it's the latter, the schematic I posted earlier is going to be quite close.
Anders M.
No, i planned to leave the tube floating, the transformer grounded to the big lead box grounded to a water pipe or something. When adjusting the filament voltage, the mains switch will be disengaged. The relay isn't going to be useless, because it is only switching a net voltage of 3.7V. However i'm worried about backflow into the arduino though, which is why i have one relay controlling another. besides, if anything goes wrong i can always kill the mains.
And yes, control unit if you have it.
Re: Grenadier's big thread of Röntgen related shenanigans
Wolfram, Wed Jun 09 2010, 11:19AM
There is still a problem. The cathode side of the X-ray tube is connected to one end of the HV-transformer, so its potential is half of the tube voltage above ground. This means that the switch part of the filament relay is also at this voltage. The arduino and the relay control and all that stuff should be at around ground potential, which means that the coil of the relay is at ground potential, and the switch part is at several tens of kilovolts. Unless the relay is a special high-isolation-voltage one, it will arc over for sure. Are you with me?
Unfortunately I don't have the schematics for any control units, but I do have a few patent numbers describing how they do the current control with a simple feedback system to control the filament transformer, if you're interested.
Anders M.
Wolfram, Wed Jun 09 2010, 11:19AM
There is still a problem. The cathode side of the X-ray tube is connected to one end of the HV-transformer, so its potential is half of the tube voltage above ground. This means that the switch part of the filament relay is also at this voltage. The arduino and the relay control and all that stuff should be at around ground potential, which means that the coil of the relay is at ground potential, and the switch part is at several tens of kilovolts. Unless the relay is a special high-isolation-voltage one, it will arc over for sure. Are you with me?
Unfortunately I don't have the schematics for any control units, but I do have a few patent numbers describing how they do the current control with a simple feedback system to control the filament transformer, if you're interested.
Anders M.
Re: Grenadier's big thread of Röntgen related shenanigans
klugesmith, Wed Jun 09 2010, 03:50PM
I'm also planning an x-ray system with battery-powered filament (one of these years).
Filament on/off control will either be opto-isolated (with a fiber!)
or use a mechanical switch actuated by a "remote" solenoid.
This: would be overkill.
klugesmith, Wed Jun 09 2010, 03:50PM
I'm also planning an x-ray system with battery-powered filament (one of these years).
Filament on/off control will either be opto-isolated (with a fiber!)
or use a mechanical switch actuated by a "remote" solenoid.
This:
would be overkill.Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Wed Jun 09 2010, 06:43PM
I thought about that, and the relay will be controlled by a battery separate from the arduino. (which is why the reed relay is in there) I really don't know of a better way to isolate then that. Even if the transformer arcs through the relay, it'll just hit the 12v gel-cell. There really shouldn't be any damage. I could even put the relay under oil, but that will slow down it's switching ability dramatically. I could even put a second reed relay to further isolate the system.
And sure, i'm interested.
Hmm, if the relay fails i'll definitely try the solenoid idea.
Just got the variac today. I like it. It lowers the output voltage nicely. It only lowers the current by 200ma at the low end. [this means 200ua on the secondary]
This is perfect. At 45kvp it should toss out 500ua heater full power. At 75(90?)kVp it should only supply 800ua.
Since more rays will be absorbed by the phosphor screen at 45 than 75(90?), less radiation is needed. Id rather have longer exposure times than short ones. This gives me more photographic control.
Anyway... i'm broke. Anyone know where i can get a lead apron free? If any of you have one, or lead sheet, i'd be willing to trade something. How about a prototype 741 ic? Or a cdv-700 geiger probe?
[Mod edit: merged triple post, use the edit button if you want to add info to a post]
Adam Munich, Wed Jun 09 2010, 06:43PM
Anders M. wrote ...
There is still a problem. The cathode side of the X-ray tube is connected to one end of the HV-transformer, so its potential is half of the tube voltage above ground. This means that the switch part of the filament relay is also at this voltage. The arduino and the relay control and all that stuff should be at around ground potential, which means that the coil of the relay is at ground potential, and the switch part is at several tens of kilovolts. Unless the relay is a special high-isolation-voltage one, it will arc over for sure. Are you with me?
Unfortunately I don't have the schematics for any control units, but I do have a few patent numbers describing how they do the current control with a simple feedback system to control the filament transformer, if you're interested.
Anders M.
There is still a problem. The cathode side of the X-ray tube is connected to one end of the HV-transformer, so its potential is half of the tube voltage above ground. This means that the switch part of the filament relay is also at this voltage. The arduino and the relay control and all that stuff should be at around ground potential, which means that the coil of the relay is at ground potential, and the switch part is at several tens of kilovolts. Unless the relay is a special high-isolation-voltage one, it will arc over for sure. Are you with me?
Unfortunately I don't have the schematics for any control units, but I do have a few patent numbers describing how they do the current control with a simple feedback system to control the filament transformer, if you're interested.
Anders M.
I thought about that, and the relay will be controlled by a battery separate from the arduino. (which is why the reed relay is in there) I really don't know of a better way to isolate then that. Even if the transformer arcs through the relay, it'll just hit the 12v gel-cell. There really shouldn't be any damage. I could even put the relay under oil, but that will slow down it's switching ability dramatically. I could even put a second reed relay to further isolate the system.
And sure, i'm interested.
Klugesmith wrote ...
I'm also planning an x-ray system with battery-powered filament (one of these years).
Filament on/off control will either be opto-isolated (with a fiber!)
or use a mechanical switch actuated by a "remote" solenoid.
This: would be overkill.
I'm also planning an x-ray system with battery-powered filament (one of these years).
Filament on/off control will either be opto-isolated (with a fiber!)
or use a mechanical switch actuated by a "remote" solenoid.
This:
would be overkill.Hmm, if the relay fails i'll definitely try the solenoid idea.
Just got the variac today. I like it. It lowers the output voltage nicely. It only lowers the current by 200ma at the low end. [this means 200ua on the secondary]
This is perfect. At 45kvp it should toss out 500ua heater full power. At 75(90?)kVp it should only supply 800ua.
Since more rays will be absorbed by the phosphor screen at 45 than 75(90?), less radiation is needed. Id rather have longer exposure times than short ones. This gives me more photographic control.
Anyway... i'm broke. Anyone know where i can get a lead apron free? If any of you have one, or lead sheet, i'd be willing to trade something. How about a prototype 741 ic? Or a cdv-700 geiger probe?
[Mod edit: merged triple post, use the edit button if you want to add info to a post]
Re: Grenadier's big thread of Röntgen related shenanigans
Wolfram, Wed Jun 09 2010, 11:13PM
The relay will still have to be controlled by the arduino, and the part between the relay and the arduino will have to stand off the full half of the tube voltage. Personally I would use a fiber optic receiver and a logic level MOSFET to switch the filament. Getting enough isolation otherwise is not particularly easy.
The patent I was talking about is US patent number 3527947, it can be viewed directly here . I don't think it's particularly useful in your case, but it gives some insight into how it's usually done, and it's a very easy way to get the tube to run at a preset current.
Anders M.
Wolfram, Wed Jun 09 2010, 11:13PM
Grenadier wrote ...
I thought about that, and the relay will be controlled by a battery separate from the arduino. (which is why the reed relay is in there) I really don't know of a better way to isolate then that. Even if the transformer arcs through the relay, it'll just hit the 12v gel-cell. There really shouldn't be any damage. I could even put the relay under oil, but that will slow down it's switching ability dramatically. I could even put a second reed relay to further isolate the system.
And sure, i'm interested.
Anders M. wrote ...
There is still a problem. The cathode side of the X-ray tube is connected to one end of the HV-transformer, so its potential is half of the tube voltage above ground. This means that the switch part of the filament relay is also at this voltage. The arduino and the relay control and all that stuff should be at around ground potential, which means that the coil of the relay is at ground potential, and the switch part is at several tens of kilovolts. Unless the relay is a special high-isolation-voltage one, it will arc over for sure. Are you with me?
Unfortunately I don't have the schematics for any control units, but I do have a few patent numbers describing how they do the current control with a simple feedback system to control the filament transformer, if you're interested.
Anders M.
There is still a problem. The cathode side of the X-ray tube is connected to one end of the HV-transformer, so its potential is half of the tube voltage above ground. This means that the switch part of the filament relay is also at this voltage. The arduino and the relay control and all that stuff should be at around ground potential, which means that the coil of the relay is at ground potential, and the switch part is at several tens of kilovolts. Unless the relay is a special high-isolation-voltage one, it will arc over for sure. Are you with me?
Unfortunately I don't have the schematics for any control units, but I do have a few patent numbers describing how they do the current control with a simple feedback system to control the filament transformer, if you're interested.
Anders M.
I thought about that, and the relay will be controlled by a battery separate from the arduino. (which is why the reed relay is in there) I really don't know of a better way to isolate then that. Even if the transformer arcs through the relay, it'll just hit the 12v gel-cell. There really shouldn't be any damage. I could even put the relay under oil, but that will slow down it's switching ability dramatically. I could even put a second reed relay to further isolate the system.
And sure, i'm interested.
The relay will still have to be controlled by the arduino, and the part between the relay and the arduino will have to stand off the full half of the tube voltage. Personally I would use a fiber optic receiver and a logic level MOSFET to switch the filament. Getting enough isolation otherwise is not particularly easy.
The patent I was talking about is US patent number 3527947, it can be viewed directly here
. I don't think it's particularly useful in your case, but it gives some insight into how it's usually done, and it's a very easy way to get the tube to run at a preset current.Anders M.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Wed Jun 09 2010, 11:32PM
Well, I'm hoping that the relay controlled by a reed relay under oil will be enough. It should, since canola oil is an excellent insulator. The oil won't affect the reed's function, being a sealed argon bubble and all, but it will insulate the switch from the solenoid.
I could always build a solenoid switch though. I might try that, and if it's reliable, i may use it. What should i use for contacts? I was thinking a light spring, like the ones in a pen.
Adam Munich, Wed Jun 09 2010, 11:32PM
wrote ...
The relay will still have to be controlled by the arduino, and the part between the relay and the arduino will have to stand off the full half of the tube voltage. Personally I would use a fiber optic receiver and a logic level MOSFET to switch the filament. Getting enough isolation otherwise is not particularly easy.
The patent I was talking about is US patent number 3527947, it can be viewed directly here . I don't think it's particularly useful in your case, but it gives some insight into how it's usually done, and it's a very easy way to get the tube to run at a preset current.
Anders M.
The relay will still have to be controlled by the arduino, and the part between the relay and the arduino will have to stand off the full half of the tube voltage. Personally I would use a fiber optic receiver and a logic level MOSFET to switch the filament. Getting enough isolation otherwise is not particularly easy.
The patent I was talking about is US patent number 3527947, it can be viewed directly here
. I don't think it's particularly useful in your case, but it gives some insight into how it's usually done, and it's a very easy way to get the tube to run at a preset current.Anders M.
Well, I'm hoping that the relay controlled by a reed relay under oil will be enough. It should, since canola oil is an excellent insulator. The oil won't affect the reed's function, being a sealed argon bubble and all, but it will insulate the switch from the solenoid.
I could always build a solenoid switch though. I might try that, and if it's reliable, i may use it. What should i use for contacts? I was thinking a light spring, like the ones in a pen.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Thu Jun 10 2010, 02:06AM
Also, my tube is made of some pretty thick brosilicate glass. I'm starting to wonder if any rays softer than 50kVp can get out...
Adam Munich, Thu Jun 10 2010, 02:06AM
Also, my tube is made of some pretty thick brosilicate glass. I'm starting to wonder if any rays softer than 50kVp can get out...
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Fri Jun 11 2010, 02:12AM
Well, i built a heatsink. It's just two heat pipes crudely soldered to a piece of copper pipe that slides over the anode bar. I'm not sure if i'm going to use it though. What i've been thinking about is putting a 12v computer fan under the oil too. Just to circulate it. It won't run fast, but it'll keep the oil floating. The last thing i want is boiling oil around the anode bar and cold oil everywhere else.
Also, does polarity matter when connecting the heater. I forgot which wire went to the hv. There's an electrostatic lens around the filament, and i'm positive if it's connected to a wire; and if it is which one.
Adam Munich, Fri Jun 11 2010, 02:12AM
Well, i built a heatsink. It's just two heat pipes crudely soldered to a piece of copper pipe that slides over the anode bar. I'm not sure if i'm going to use it though. What i've been thinking about is putting a 12v computer fan under the oil too. Just to circulate it. It won't run fast, but it'll keep the oil floating. The last thing i want is boiling oil around the anode bar and cold oil everywhere else.
Also, does polarity matter when connecting the heater. I forgot which wire went to the hv. There's an electrostatic lens around the filament, and i'm positive if it's connected to a wire; and if it is which one.
Re: Grenadier's big thread of Röntgen related shenanigans
Hon1nbo, Fri Jun 11 2010, 02:26AM
just thought I'd throw this in here: a possible reason why the resistor gives a different current is because you may not have a proper resistance reading for the bulb, as it changes as the heat increases IIRC
also, for isolation, use fiber optics, it can be done for cheap, it's reliable, easy to modify and maintain (unlike an oil bath), etc
Also, if your in the US check Craigslist for things like lead shielding etc, at least here X-Ray hardware shows up at least a few times a month (sometimes a lot of listings at once!).
-Jimmy
Hon1nbo, Fri Jun 11 2010, 02:26AM
just thought I'd throw this in here: a possible reason why the resistor gives a different current is because you may not have a proper resistance reading for the bulb, as it changes as the heat increases IIRC
also, for isolation, use fiber optics, it can be done for cheap, it's reliable, easy to modify and maintain (unlike an oil bath), etc
Also, if your in the US check Craigslist for things like lead shielding etc, at least here X-Ray hardware shows up at least a few times a month (sometimes a lot of listings at once!).
-Jimmy
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Fri Jun 11 2010, 02:45AM
1) The resistance of a half-hot bulb is 72 ohms, when the transformer draws more current, it raises the resistance to a maximum of 144 ohms. A resistor does not.
2) If i solve the voltage spike problem, i won't even need to switch the filament.
3) I've been looking. No luck.
Adam Munich, Fri Jun 11 2010, 02:45AM
1) The resistance of a half-hot bulb is 72 ohms, when the transformer draws more current, it raises the resistance to a maximum of 144 ohms. A resistor does not.
2) If i solve the voltage spike problem, i won't even need to switch the filament.
3) I've been looking. No luck.
Re: Grenadier's big thread of Röntgen related shenanigans
Wolfram, Fri Jun 11 2010, 07:23AM
Your tube is pretty typical as far as dental tubes go, and the glass will mabe block everything under 25-30kV.
I don't think you need to worry very much about cooling. Dental X-ray heads often run the tube at close to a kilowatt without any means to circulate the oil except for convection, so I don't think your design will need any artificial way to get oil circulation either. Not even the largest medical tubes running much higher powers need fans to circulate the oil. Convection does a very good job.
Also, stop posting multiple posts in a row, it's against the rules. Use the edit button instead.
Anders M.
Wolfram, Fri Jun 11 2010, 07:23AM
Your tube is pretty typical as far as dental tubes go, and the glass will mabe block everything under 25-30kV.
I don't think you need to worry very much about cooling. Dental X-ray heads often run the tube at close to a kilowatt without any means to circulate the oil except for convection, so I don't think your design will need any artificial way to get oil circulation either. Not even the largest medical tubes running much higher powers need fans to circulate the oil. Convection does a very good job.
Also, stop posting multiple posts in a row, it's against the rules. Use the edit button instead.
Anders M.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Fri Jun 11 2010, 01:59PM
Sorry.
However my tube is rated at only 75kvp@2mA. That's only 75Watts. I just don't want to break it.
Anyway, i'm livid. I got some lcd's in the mail, one for the ray, one for my geiger counter, and they're junk. The guy wants me to mail them back to china, but i'm not paying $20. I hope paypal can get me a refund.
Adam Munich, Fri Jun 11 2010, 01:59PM
Sorry.
However my tube is rated at only 75kvp@2mA. That's only 75Watts. I just don't want to break it.
Anyway, i'm livid. I got some lcd's in the mail, one for the ray, one for my geiger counter, and they're junk. The guy wants me to mail them back to china, but i'm not paying $20. I hope paypal can get me a refund.
Re: Grenadier's big thread of Röntgen related shenanigans
Wolfram, Fri Jun 11 2010, 04:48PM
That's 150 watts, and that's the continous rating. These tubes are usually used at several times the continous power rating, as they are used for short durations. A dental exposure is usually under two seconds, unless it is a pantomographic unit, with those the exposure times can be as long as 20 seconds. The datasheets for the tubes usually give curves for maximum allowable power, but datasheets are usually very hard to find for most tubes, so I usually just find the datasheet for a tube with similar ratings and size, to get a general idea. This should be somewhere in the same area, and should give you a general idea.
In any case, running it at 75W like you plan on doing will allow you to run it indefinitely. Taking x-ray pictures with intensifying cassettes should not require too much energy (unless you are running the tube on such a low voltage that almost all of the radiation is stopped by the glass), so I doubt you'll even be able to measure temperature rise in the oil after an exposure. This is why I think a fan to circulate the oil is largely uneccessary.
Anders M.
Wolfram, Fri Jun 11 2010, 04:48PM
That's 150 watts, and that's the continous rating. These tubes are usually used at several times the continous power rating, as they are used for short durations. A dental exposure is usually under two seconds, unless it is a pantomographic unit, with those the exposure times can be as long as 20 seconds. The datasheets for the tubes usually give curves for maximum allowable power, but datasheets are usually very hard to find for most tubes, so I usually just find the datasheet for a tube with similar ratings and size, to get a general idea. This
should be somewhere in the same area, and should give you a general idea.In any case, running it at 75W like you plan on doing will allow you to run it indefinitely. Taking x-ray pictures with intensifying cassettes should not require too much energy (unless you are running the tube on such a low voltage that almost all of the radiation is stopped by the glass), so I doubt you'll even be able to measure temperature rise in the oil after an exposure. This is why I think a fan to circulate the oil is largely uneccessary.
Anders M.
Re: Grenadier's big thread of Röntgen related shenanigans
Proud Mary, Fri Jun 11 2010, 06:15PM
At a distance of 1 metre in the beam from a 75kV/2mA X-ray tube, the dose rate will be 32 Sv/hr.
We'll call this 0.5 Sv/minute to make life easy, since there is nothing very exact about the acute effects of radiation poisoning.
After 4 minutes, you will suffer 'mild' radiation poisoning, featuring nausea and vomiting within 24 hrs.
After 6 minutes, you can add general malaise, bloody stools, bloody vomit, and subsequent hair loss.
After 12 to 16 minutes, you will suffer all the previous within 30 minutes, plus high fever, vertigo, mental confusion, organ failure, collapse of blood pressure, and death in 50% of cases.
Long term consequences are to be expected among survivors of acute exposure, though some of these may take years to develop.
Repeated exposure to even very low doses is linked to various sorts of cancer in dental workers, despite their using all recommended screens, shields and aprons.
You may harm not just yourself, but innocent people and animals living above, below, and on either side of you.
And that's all I have to say on the matter.
Proud Mary, Fri Jun 11 2010, 06:15PM
At a distance of 1 metre in the beam from a 75kV/2mA X-ray tube, the dose rate will be 32 Sv/hr.
We'll call this 0.5 Sv/minute to make life easy, since there is nothing very exact about the acute effects of radiation poisoning.
After 4 minutes, you will suffer 'mild' radiation poisoning, featuring nausea and vomiting within 24 hrs.
After 6 minutes, you can add general malaise, bloody stools, bloody vomit, and subsequent hair loss.
After 12 to 16 minutes, you will suffer all the previous within 30 minutes, plus high fever, vertigo, mental confusion, organ failure, collapse of blood pressure, and death in 50% of cases.
Long term consequences are to be expected among survivors of acute exposure, though some of these may take years to develop.
Repeated exposure to even very low doses is linked to various sorts of cancer in dental workers, despite their using all recommended screens, shields and aprons.
You may harm not just yourself, but innocent people and animals living above, below, and on either side of you.
And that's all I have to say on the matter.
Re: Grenadier's big thread of Röntgen related shenanigans
Wolfram, Sat Jun 12 2010, 01:50AM
I don't think scare numbers are neccessary here, as Grenadier has already shown in the other thread that he respects the dangers of x-rays and that he has built a 4mm thick lead box to contain the whole experiment in. He is also planning on being several hundred feet away when the tube is powered, so I think any radiation exposure he will get from this will be immeasurable compared to background radiation.
Of course it's important to respect the dangers of x-rays, though most of the hobbies discussed here have very real dangers, and when the dangers are understood and safety precautions are taken, working with x-rays can be as safe as any other hobby.
Anders M.
Wolfram, Sat Jun 12 2010, 01:50AM
I don't think scare numbers are neccessary here, as Grenadier has already shown in the other thread that he respects the dangers of x-rays and that he has built a 4mm thick lead box to contain the whole experiment in. He is also planning on being several hundred feet away when the tube is powered, so I think any radiation exposure he will get from this will be immeasurable compared to background radiation.
Of course it's important to respect the dangers of x-rays, though most of the hobbies discussed here have very real dangers, and when the dangers are understood and safety precautions are taken, working with x-rays can be as safe as any other hobby.
Anders M.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Sat Jun 12 2010, 02:11AM
@Anders
Good to know. Sorry for the silly calc mistake. I'm going to take pictures 3 ways;
1) with kodak paper and intensifying screen pressed to it.
2) Using a europium glow in the dark screen. The long lasting phosphor should "build up enough light" let a camera inside take a picture.
@Proud Mary
I'm sorry for the big pic. Idk how to shrink it.
@Anders again
Thanks for the support.
[Edit: Now click the edit button and learn how to do it]
Adam Munich, Sat Jun 12 2010, 02:11AM
@Anders
Good to know. Sorry for the silly calc mistake. I'm going to take pictures 3 ways;
1) with kodak paper and intensifying screen pressed to it.
2) Using a europium glow in the dark screen. The long lasting phosphor should "build up enough light" let a camera inside take a picture.
@Proud Mary
I'm sorry for the big pic. Idk how to shrink it.
@Anders again
Thanks for the support.
[Edit: Now click the edit button and learn how to do it]
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Sat Jun 12 2010, 05:47PM
I built an isolation relay. However, i'm starting to wonder if it's safe to turn on the hv before warming up the tube. I won't need this relay if my hot-bulb design works though. However i can't build it yet; my relay and other parts from bgmicro are still in the mail.
Adam Munich, Sat Jun 12 2010, 05:47PM
I built an isolation relay. However, i'm starting to wonder if it's safe to turn on the hv before warming up the tube. I won't need this relay if my hot-bulb design works though. However i can't build it yet; my relay and other parts from bgmicro are still in the mail.
Re: Grenadier's big thread of Röntgen related shenanigans
Proud Mary, Sat Jun 12 2010, 09:22PM
You may damage the tube by so-called 'cathode stripping' or internal flash-over if you apply anode voltage before the filament or cathode is thoroughly warmed. Further, if you are using a self-rectified circuit, damaging reverse conduction may occur.
Moreover, a tube which is either brand new, or has been out of service for some time, must be 'seasoned' before the full anode voltage is applied. The point of 'seasoning' is to re-absorb gas molecules which have cast adrift whilst the tube has been out of service. 'Seasoning' consists of the application of HT in a graduated sequence of increments over a period of time. By way of illustration only, and not recommendation, (since I know nothing of your tube, or its history) three one minute applications of 10kV with one minute between each, three applications of 15kV for a minute each with one minute intervals, three applications of 20kV, and so on in steps until you reach the full working voltage.
Different manufacturers have differing 'seasoning' recommendations, but all share the common principle of a graduated series of rising voltage steps before the full anode voltage is applied. The longer a tube has been out of service, the more thoroughly must the 'seasoning' procedure be performed. Light seasoning should be performed if a tube has been out of service for 3 - 6 months, with a longer, slower and more gradual procedure for 6 - 12 months, and so on.
Proud Mary, Sat Jun 12 2010, 09:22PM
Grenadier wrote ...
i'm starting to wonder if it's safe to turn on the hv before warming up the tube.
i'm starting to wonder if it's safe to turn on the hv before warming up the tube.
You may damage the tube by so-called 'cathode stripping' or internal flash-over if you apply anode voltage before the filament or cathode is thoroughly warmed. Further, if you are using a self-rectified circuit, damaging reverse conduction may occur.
Moreover, a tube which is either brand new, or has been out of service for some time, must be 'seasoned' before the full anode voltage is applied. The point of 'seasoning' is to re-absorb gas molecules which have cast adrift whilst the tube has been out of service. 'Seasoning' consists of the application of HT in a graduated sequence of increments over a period of time. By way of illustration only, and not recommendation, (since I know nothing of your tube, or its history) three one minute applications of 10kV with one minute between each, three applications of 15kV for a minute each with one minute intervals, three applications of 20kV, and so on in steps until you reach the full working voltage.
Different manufacturers have differing 'seasoning' recommendations, but all share the common principle of a graduated series of rising voltage steps before the full anode voltage is applied. The longer a tube has been out of service, the more thoroughly must the 'seasoning' procedure be performed. Light seasoning should be performed if a tube has been out of service for 3 - 6 months, with a longer, slower and more gradual procedure for 6 - 12 months, and so on.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Sat Jun 12 2010, 10:28PM
A) Wow, i really hope my keep-lightbulb-warm circuit will work now.
B) I read about seasoning and thought it would "cover itself", because i was going to start using the tube at a low voltage, and gradually build up my courage to bring it up. :) Now i know to start even lower. This could take a long time, and it should, because this tube hasn't been used in 10 years. I know it's vacuum is good though, because i tested it at 24v, 20ma as a thermionic diode.
More tube info;
Dunlee mfct 197?
Seems to be brosilicate glass.
Very minor browning.
Very tiny pits on anode, with a minor crack in an H shape.
75kVp max
2mA max
Heater white hot at 3.5v
Also... does filament polarity matter? I'm not sure if the electrostatic lens is hooked up to a wire, and if it is which one.
Adam Munich, Sat Jun 12 2010, 10:28PM
A) Wow, i really hope my keep-lightbulb-warm circuit will work now.
B) I read about seasoning and thought it would "cover itself", because i was going to start using the tube at a low voltage, and gradually build up my courage to bring it up. :) Now i know to start even lower. This could take a long time, and it should, because this tube hasn't been used in 10 years. I know it's vacuum is good though, because i tested it at 24v, 20ma as a thermionic diode.
More tube info;
Dunlee mfct 197?
Seems to be brosilicate glass.
Very minor browning.
Very tiny pits on anode, with a minor crack in an H shape.
75kVp max
2mA max
Heater white hot at 3.5v
Also... does filament polarity matter? I'm not sure if the electrostatic lens is hooked up to a wire, and if it is which one.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Sun Jun 13 2010, 12:14AM
New schematic. I had to shorten the length of wire because the longest cord i have is 250ft. So now, a lead apron is not a must, but i'm going to wear one. As i said before, "real" lead aprons are pathetic, they only give .5mm protection. I'm going to make my own from some 1mm sheet. I'll see if i can get some from local roofing companies. I really don't want to pay $80 for 6sqft. online.
Adam Munich, Sun Jun 13 2010, 12:14AM
New schematic. I had to shorten the length of wire because the longest cord i have is 250ft. So now, a lead apron is not a must, but i'm going to wear one. As i said before, "real" lead aprons are pathetic, they only give .5mm protection. I'm going to make my own from some 1mm sheet. I'll see if i can get some from local roofing companies. I really don't want to pay $80 for 6sqft. online.
Re: Grenadier's big thread of Röntgen related shenanigans
IntraWinding, Sun Jun 13 2010, 12:21AM
Could you dig a hole in the ground for your experiments so you get hundreds of feet of earth protecting you, and avoid lead poisoning too?
IntraWinding, Sun Jun 13 2010, 12:21AM
Could you dig a hole in the ground for your experiments so you get hundreds of feet of earth protecting you, and avoid lead poisoning too?
Re: Grenadier's big thread of Röntgen related shenanigans
Proud Mary, Sun Jun 13 2010, 12:36AM
You should plan to control the anode current by adjusting the heater voltage, for which you need a fairly 'stiff' EHT supply. It's no good if the anode voltage begins to fall when you increase the current due to an inadequate supply. I would suggest you start at 1.5V on the heater or filament , and gradually increase it until the tube's 2mA max is reached. Excess heater voltage is probably the quickest way of destroying a tube. I use a single Hawker Cyclon 2V 8AH lead acid cell (which has the same proportions as a standard "D" cell, but is rather larger) which is easy to 'float' at -20kv to -40kV in grounded anode configurations, compared with the problems of having a transformer which can hold of such voltages on its LT windings. Other advantages of using a single 2V cell is that the heater voltage cannot rise no matter what happens elsewhere in the circuit, and that no matter what may happen the production of X-rays will shut down in a few hours when the battery is discharged.
Once you have the apparatus running, you should make an X-ray pinhole camera in order to visualize the anode focal spot to see that all is right with the focusing cup potential.
Making all these adjustments and preliminary tests without compromising the shielding is time consuming.
Proud Mary, Sun Jun 13 2010, 12:36AM
Grenadier wrote ...
Heater white hot at 3.5v
Heater white hot at 3.5v
You should plan to control the anode current by adjusting the heater voltage, for which you need a fairly 'stiff' EHT supply. It's no good if the anode voltage begins to fall when you increase the current due to an inadequate supply. I would suggest you start at 1.5V on the heater or filament , and gradually increase it until the tube's 2mA max is reached. Excess heater voltage is probably the quickest way of destroying a tube. I use a single Hawker Cyclon 2V 8AH lead acid cell (which has the same proportions as a standard "D" cell, but is rather larger) which is easy to 'float' at -20kv to -40kV in grounded anode configurations, compared with the problems of having a transformer which can hold of such voltages on its LT windings. Other advantages of using a single 2V cell is that the heater voltage cannot rise no matter what happens elsewhere in the circuit, and that no matter what may happen the production of X-rays will shut down in a few hours when the battery is discharged.
Once you have the apparatus running, you should make an X-ray pinhole camera in order to visualize the anode focal spot to see that all is right with the focusing cup potential.
Making all these adjustments and preliminary tests without compromising the shielding is time consuming.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Sun Jun 13 2010, 01:30AM
@ IntraWinding
No. I could, but this box weighs 100lbs. If i put it in a hole, it's never coming out. Besides, i'll put my house in between me and the box too. Even though it's not, Sheetrock is better than nothing.
@ proudmary
I'm using a 3.7v lithium cell with a rheostat to control the heater current/temperature. I planned on adjusting that by a dial on the machine which i'll put a calibrated label on. Then i get well out of the way and the 0-120v is fed into the machine. This will warm up the lightbulb for a second, then a relay will switch feeding the current through the lightbulb through the transformer. By this method, the transformer is incapable of supplying more than .8ma, even when shorted. This way, i cant overheat the tube by accident. A longer exposure is better anyway; it gives more photographic control. After the exposure, i'll flip a switch or maybe two cutting off the mains and another turning off the arduino/12v supply, making sure it can't possibly expose while i'm adjusting it.
I'm building this thing with safety in mind, not accuracy. If the kVp drops with higher currents, so be it. I'll develop the photo and if it looks like crap, i'll turn up the variac.
X-ray pinhole camera? Explain please. I was just going to make images directly, just by placing an object in front of the intensifying screen. If it was blurry, then i probably have the heater wires backward and reverse them. I'm well aware how x-rays are produced/scattered/absorbed with the bremsstrahlung and compton scattering etc. However i'm still not too clear on how the focusing cup works. Does it lose focus at lower than intended kVps? My tube is of the 3 wire type.
FYI, it's going to be a self-rectifying circuit.
Adam Munich, Sun Jun 13 2010, 01:30AM
@ IntraWinding
No. I could, but this box weighs 100lbs. If i put it in a hole, it's never coming out. Besides, i'll put my house in between me and the box too. Even though it's not, Sheetrock is better than nothing.
@ proudmary
I'm using a 3.7v lithium cell with a rheostat to control the heater current/temperature. I planned on adjusting that by a dial on the machine which i'll put a calibrated label on. Then i get well out of the way and the 0-120v is fed into the machine. This will warm up the lightbulb for a second, then a relay will switch feeding the current through the lightbulb through the transformer. By this method, the transformer is incapable of supplying more than .8ma, even when shorted. This way, i cant overheat the tube by accident. A longer exposure is better anyway; it gives more photographic control. After the exposure, i'll flip a switch or maybe two cutting off the mains and another turning off the arduino/12v supply, making sure it can't possibly expose while i'm adjusting it.
I'm building this thing with safety in mind, not accuracy. If the kVp drops with higher currents, so be it. I'll develop the photo and if it looks like crap, i'll turn up the variac.
X-ray pinhole camera? Explain please. I was just going to make images directly, just by placing an object in front of the intensifying screen. If it was blurry, then i probably have the heater wires backward and reverse them. I'm well aware how x-rays are produced/scattered/absorbed with the bremsstrahlung and compton scattering etc. However i'm still not too clear on how the focusing cup works. Does it lose focus at lower than intended kVps? My tube is of the 3 wire type.
FYI, it's going to be a self-rectifying circuit.
Re: Grenadier's big thread of Röntgen related shenanigans
Proud Mary, Sun Jun 13 2010, 08:26AM
X-rays behave like visible light when they transit a pinhole.
If you make the smallest, most accurate pinhole you can in a lead or tungsten sheet, centre it in the beam half way between the anode and your film, and ensure that it is exactly at right angles to the beam with a plumb bob and triangle, then an image of the focal spot on the anode will be obtained, whose width can be measured directly.
You will also see directly what effect, if any, the pitting and cracking of the target has had.
Pinhole cameras are one of the key tools in X-ray astronomy. Arrays of pinhole cameras have been fitted to space craft to produce X-ray images of the universe.
Proud Mary, Sun Jun 13 2010, 08:26AM
Grenadier wrote ...
X-ray pinhole camera? Explain please.
X-ray pinhole camera? Explain please.
X-rays behave like visible light when they transit a pinhole.
If you make the smallest, most accurate pinhole you can in a lead or tungsten sheet, centre it in the beam half way between the anode and your film, and ensure that it is exactly at right angles to the beam with a plumb bob and triangle, then an image of the focal spot on the anode will be obtained, whose width can be measured directly.
You will also see directly what effect, if any, the pitting and cracking of the target has had.
Pinhole cameras are one of the key tools in X-ray astronomy. Arrays of pinhole cameras have been fitted to space craft to produce X-ray images of the universe.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Sun Jun 13 2010, 01:34PM
I'll have to try it. It probably requires a long exposure.
Adam Munich, Sun Jun 13 2010, 01:34PM
I'll have to try it. It probably requires a long exposure.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Mon Jun 14 2010, 01:58AM
Assuming worst case scenario of 100kv...
HVL of Pb for 100kv is .27mm
Thinnest part of box is 3.6mm
3.6/.27 = 13.3333...
so;
100% penetration, halved 13 times = 0.00162760417%
.0016% ...That gives me some confidence :)
So, with a value of...
1sievert/min inside box * .0016 = 160mrem/min directly in front of the thing. Not safe, but manageable.
So if i'm 200ft away, w/o shielding, inverse square law dictates that it'll be .004millirem/min. or .24mr/hr. That's not negligable, but it's safe because this thing will only be on for fractions of a minute once every 20 minutes or so.
.004mr/m = 0.00006 mr/s
0.00006 mr/s * 10s = 0.0006 mr/longexposure without apron.
so 20 exposures = 0.012millirem
Hmm, lets add the 1mm lead apron, or roughly 3 halving thicknesses.
.0006mr/exp /3 = 0.0002mrem/exposure with apron
If i make 20 exposures every day for an entire year (ridiculous) that would work out to be 1.46 millirem a year + background. Since a smoker gets roughly 270mrem a year, i think i designed a pretty damn safe machine.
This is all in the beam path. I'll be behind the tube, so values should be even lower.
Please correct me if i screwed up somewhere. That's alot of math at 10pm.
Adam Munich, Mon Jun 14 2010, 01:58AM
Assuming worst case scenario of 100kv...
HVL of Pb for 100kv is .27mm
Thinnest part of box is 3.6mm
3.6/.27 = 13.3333...
so;
100% penetration, halved 13 times = 0.00162760417%
.0016% ...That gives me some confidence :)
So, with a value of...
1sievert/min inside box * .0016 = 160mrem/min directly in front of the thing. Not safe, but manageable.
So if i'm 200ft away, w/o shielding, inverse square law dictates that it'll be .004millirem/min. or .24mr/hr. That's not negligable, but it's safe because this thing will only be on for fractions of a minute once every 20 minutes or so.
.004mr/m = 0.00006 mr/s
0.00006 mr/s * 10s = 0.0006 mr/longexposure without apron.
so 20 exposures = 0.012millirem
Hmm, lets add the 1mm lead apron, or roughly 3 halving thicknesses.
.0006mr/exp /3 = 0.0002mrem/exposure with apron
If i make 20 exposures every day for an entire year (ridiculous) that would work out to be 1.46 millirem a year + background. Since a smoker gets roughly 270mrem a year, i think i designed a pretty damn safe machine.
This is all in the beam path. I'll be behind the tube, so values should be even lower.
Please correct me if i screwed up somewhere. That's alot of math at 10pm.
Re: Grenadier's big thread of Röntgen related shenanigans
Wolfram, Mon Jun 14 2010, 06:06AM
And even that is assuming all of the energy is at 100keV, when in reality, very little energy will be at the peak voltage. I think the average photon energy will be around a third of the peak photon energy, but to actually calculate the amount of radiation that gets through the shielding is not as simple. You can always do like you did and assume all of the photons are at the peak voltage, then you'll know that you get a very conservative rating. This is the way RadPro does it too.
Where did you get the 1Sv/min figure from?
Anders M.
Wolfram, Mon Jun 14 2010, 06:06AM
And even that is assuming all of the energy is at 100keV, when in reality, very little energy will be at the peak voltage. I think the average photon energy will be around a third of the peak photon energy, but to actually calculate the amount of radiation that gets through the shielding is not as simple. You can always do like you did and assume all of the photons are at the peak voltage, then you'll know that you get a very conservative rating. This is the way RadPro does it too.
Where did you get the 1Sv/min figure from?
Anders M.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Mon Jun 14 2010, 02:52PM
Well, since proud mary's estimate was .5sv at a meter, the distance from the tube to the far wall of the box is about .5m So 4sv/min. But i will only be running the tube at 1/4 max power, 1sv/min. It was really a complete guess. :) And you're right, it will be at 50kv most of the time whose HVL is .06mm. I'll never take it past 70kvp anyway.
Also, the actual thinnest part of the box is the gaps between the lip and he lid, i put 1mm lead tape there. I'll put on another 1mm. I designed it so the gaps face upward, so any stray rays can only hit a bird or some mosquitoes. (i don't live in appt, and it'll be outside)
The box's gaps are completely sealed withe the so-called welds. Pic on other thread. I couldn't do that for the lid because it wouldn't fit on if i did.
Adam Munich, Mon Jun 14 2010, 02:52PM
Well, since proud mary's estimate was .5sv at a meter, the distance from the tube to the far wall of the box is about .5m So 4sv/min. But i will only be running the tube at 1/4 max power, 1sv/min. It was really a complete guess. :) And you're right, it will be at 50kv most of the time whose HVL is .06mm. I'll never take it past 70kvp anyway.
Also, the actual thinnest part of the box is the gaps between the lip and he lid, i put 1mm lead tape there. I'll put on another 1mm. I designed it so the gaps face upward, so any stray rays can only hit a bird or some mosquitoes. (i don't live in appt, and it'll be outside)
The box's gaps are completely sealed withe the so-called welds. Pic on other thread. I couldn't do that for the lid because it wouldn't fit on if i did.
Re: Grenadier's big thread of Röntgen related shenanigans
Proud Mary, Mon Jun 14 2010, 03:41PM
With Va = 50kVp, Ia = 0.5mA, the dose rate at 1 metre centre beam will be about 6 Sv/hr.
With 4.6mm Pb shielding (3.6mm box, plus 1mm apron) the dose rate at 1 metre will fall to about 0.001 uSv/hr.
Proud Mary, Mon Jun 14 2010, 03:41PM
Grenadier wrote ...
Well, since proud mary's estimate was .5sv at a meter, the distance from the tube to the far wall of the box is about .5m So 4sv/min. But i will only be running the tube at 1/4 max power, 1sv/min. It was really a complete guess. :) And you're right, it will be at 50kv most of the time whose HVL is .06mm. I'll never take it past 70kvp anyway.
Well, since proud mary's estimate was .5sv at a meter, the distance from the tube to the far wall of the box is about .5m So 4sv/min. But i will only be running the tube at 1/4 max power, 1sv/min. It was really a complete guess. :) And you're right, it will be at 50kv most of the time whose HVL is .06mm. I'll never take it past 70kvp anyway.
With Va = 50kVp, Ia = 0.5mA, the dose rate at 1 metre centre beam will be about 6 Sv/hr.
With 4.6mm Pb shielding (3.6mm box, plus 1mm apron) the dose rate at 1 metre will fall to about 0.001 uSv/hr.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Mon Jun 14 2010, 03:43PM
good to know.
edit:
ugh, my rheostat just came and it has too much resistance. It's 0-25 ohm and it turns out i need a 5 ohm. Oh well, i suppose i can just use it to control the heater anyway, even if everything from white hot to cold is on 1/8 of a turn.
Adam Munich, Mon Jun 14 2010, 03:43PM
good to know.
edit:
ugh, my rheostat just came and it has too much resistance. It's 0-25 ohm and it turns out i need a 5 ohm. Oh well, i suppose i can just use it to control the heater anyway, even if everything from white hot to cold is on 1/8 of a turn.
Re: Grenadier's big thread of Röntgen related shenanigans
Wolfram, Mon Jun 14 2010, 10:54PM
I don't think those numbers are entirely correct.
I tried running those same numbers through RadPro, I don't know if that's what you used. It gave me 5.85 Sv/hr when I selected only 1mm of beryllium filtration in the beam, and the same conditions as you used (50kV, 0.5mA, 100cm). Since Grenadiers tube is not a beryllium window tube, these numbers are a lot higher than they should be. I'm not sure how much filtration the glass of his tube offers, but glass filtration for dental tubes is often quoted as equivalent to around 0.8mm of aluminium. Example: . RadPro doesn't let me add an arbitrary aluminium filter thickness, there are only a few choices, but if I add 0.5mm of aluminium filtration, I get just under 0.35 Sv/hr, or about 1/15 of the previous quote. If I select 1mm of aluminium filtration, I get just about half of that again, so I guess it's somewhere in between those two. It's quite stunning how much difference the glass filtration makes.
Edit: and with the 4.6mm lead shielding it will be down to about 0.064 nSv/hr according to RadPro, or over 4000 times less than background radiation. Bear in mind that this is a meter from the tube. Factoring in the 400' Grenadier said he would be from the experiment, we are talking about 120 million times less than background. Upping the tube voltage to 70kV increases the dose dramatically, to only 40 times less than background. For a one minute exposure, the added radiation dose you will receive is equal the background dose you get from living for 1.5 seconds. Or flying in an airplane for about 140 milliseconds. And even this is assumin the tube is pointing at you inside the box, through it's thinnest point, running at 70kV, and probably with less calculated inherent shielding from the glass than in reality (as RadPro only let me select 0.5mm). And even then, RadPro is made to over-estimate. I'm therefore pretty confident in saying that you are pretty safe with all the precautions you're taking, and to be honest, I think all the working with lead will harm you much more in the long run. Assuming all the safety precautions you mentioned are used, of course.
Anders M.
Wolfram, Mon Jun 14 2010, 10:54PM
Proud Mary wrote ...
With Va = 50kVp, Ia = 0.5mA, the dose rate at 1 metre centre beam will be about 6 Sv/hr.
With 4.6mm Pb shielding (3.6mm box, plus 1mm apron) the dose rate at 1 metre will fall to about 0.001 uSv/hr.
Grenadier wrote ...
Well, since proud mary's estimate was .5sv at a meter, the distance from the tube to the far wall of the box is about .5m So 4sv/min. But i will only be running the tube at 1/4 max power, 1sv/min. It was really a complete guess. :) And you're right, it will be at 50kv most of the time whose HVL is .06mm. I'll never take it past 70kvp anyway.
Well, since proud mary's estimate was .5sv at a meter, the distance from the tube to the far wall of the box is about .5m So 4sv/min. But i will only be running the tube at 1/4 max power, 1sv/min. It was really a complete guess. :) And you're right, it will be at 50kv most of the time whose HVL is .06mm. I'll never take it past 70kvp anyway.
With Va = 50kVp, Ia = 0.5mA, the dose rate at 1 metre centre beam will be about 6 Sv/hr.
With 4.6mm Pb shielding (3.6mm box, plus 1mm apron) the dose rate at 1 metre will fall to about 0.001 uSv/hr.
I don't think those numbers are entirely correct.
I tried running those same numbers through RadPro, I don't know if that's what you used. It gave me 5.85 Sv/hr when I selected only 1mm of beryllium filtration in the beam, and the same conditions as you used (50kV, 0.5mA, 100cm). Since Grenadiers tube is not a beryllium window tube, these numbers are a lot higher than they should be. I'm not sure how much filtration the glass of his tube offers, but glass filtration for dental tubes is often quoted as equivalent to around 0.8mm of aluminium. Example:
. RadPro doesn't let me add an arbitrary aluminium filter thickness, there are only a few choices, but if I add 0.5mm of aluminium filtration, I get just under 0.35 Sv/hr, or about 1/15 of the previous quote. If I select 1mm of aluminium filtration, I get just about half of that again, so I guess it's somewhere in between those two. It's quite stunning how much difference the glass filtration makes. Edit: and with the 4.6mm lead shielding it will be down to about 0.064 nSv/hr according to RadPro, or over 4000 times less than background radiation. Bear in mind that this is a meter from the tube. Factoring in the 400' Grenadier said he would be from the experiment, we are talking about 120 million times less than background. Upping the tube voltage to 70kV increases the dose dramatically, to only 40 times less than background. For a one minute exposure, the added radiation dose you will receive is equal the background dose you get from living for 1.5 seconds. Or flying in an airplane for about 140 milliseconds. And even this is assumin the tube is pointing at you inside the box, through it's thinnest point, running at 70kV, and probably with less calculated inherent shielding from the glass than in reality (as RadPro only let me select 0.5mm). And even then, RadPro is made to over-estimate. I'm therefore pretty confident in saying that you are pretty safe with all the precautions you're taking, and to be honest, I think all the working with lead will harm you much more in the long run. Assuming all the safety precautions you mentioned are used, of course.
Anders M.
Re: Grenadier's big thread of Röntgen related shenanigans
Proud Mary, Mon Jun 14 2010, 11:10PM
Your knowledge and practical experience are clearly so much greater than mine, Anders, that I have no hesitation in leaving Mr McGoo in your capable hands.
Proud Mary, Mon Jun 14 2010, 11:10PM
Anders M. wrote ...
I don't think those numbers are entirely correct.
I tried running those same numbers through RadPro, I don't know if that's what you used. It gave me 5.85 Sv/hr when I selected only 1mm of beryllium filtration in the beam, and the same conditions as you used (50kV, 0.5mA, 100cm). Since Grenadiers tube is not a beryllium window tube, these numbers are a lot higher than they should be. I'm not sure how much filtration the glass of his tube offers, but glass filtration for dental tubes is often quoted as equivalent to around 0.8mm of aluminium. Example: . RadPro doesn't let me add an arbitrary aluminium filter thickness, there are only a few choices, but if I add 0.5mm of aluminium filtration, I get just under 0.35 Sv/hr, or about 1/15 of the previous quote. If I select 1mm of aluminium filtration, I get just about half of that again, so I guess it's somewhere in between those two. It's quite stunning how much difference the glass filtration makes.
Proud Mary wrote ...
With Va = 50kVp, Ia = 0.5mA, the dose rate at 1 metre centre beam will be about 6 Sv/hr.
With 4.6mm Pb shielding (3.6mm box, plus 1mm apron) the dose rate at 1 metre will fall to about 0.001 uSv/hr.
Grenadier wrote ...
Well, since proud mary's estimate was .5sv at a meter, the distance from the tube to the far wall of the box is about .5m So 4sv/min. But i will only be running the tube at 1/4 max power, 1sv/min. It was really a complete guess. :) And you're right, it will be at 50kv most of the time whose HVL is .06mm. I'll never take it past 70kvp anyway.
Well, since proud mary's estimate was .5sv at a meter, the distance from the tube to the far wall of the box is about .5m So 4sv/min. But i will only be running the tube at 1/4 max power, 1sv/min. It was really a complete guess. :) And you're right, it will be at 50kv most of the time whose HVL is .06mm. I'll never take it past 70kvp anyway.
With Va = 50kVp, Ia = 0.5mA, the dose rate at 1 metre centre beam will be about 6 Sv/hr.
With 4.6mm Pb shielding (3.6mm box, plus 1mm apron) the dose rate at 1 metre will fall to about 0.001 uSv/hr.
I don't think those numbers are entirely correct.
I tried running those same numbers through RadPro, I don't know if that's what you used. It gave me 5.85 Sv/hr when I selected only 1mm of beryllium filtration in the beam, and the same conditions as you used (50kV, 0.5mA, 100cm). Since Grenadiers tube is not a beryllium window tube, these numbers are a lot higher than they should be. I'm not sure how much filtration the glass of his tube offers, but glass filtration for dental tubes is often quoted as equivalent to around 0.8mm of aluminium. Example:
. RadPro doesn't let me add an arbitrary aluminium filter thickness, there are only a few choices, but if I add 0.5mm of aluminium filtration, I get just under 0.35 Sv/hr, or about 1/15 of the previous quote. If I select 1mm of aluminium filtration, I get just about half of that again, so I guess it's somewhere in between those two. It's quite stunning how much difference the glass filtration makes. Your knowledge and practical experience are clearly so much greater than mine, Anders, that I have no hesitation in leaving Mr McGoo in your capable hands.
Re: Grenadier's big thread of Röntgen related shenanigans
Wolfram, Mon Jun 14 2010, 11:18PM
I'm not sure if that is sarcasm, Proud Mary, I certainly hope not, as I was just pointing out an error in your calculation. I'm not sure what experience or knowledge has to do with this.
Anders M.
Wolfram, Mon Jun 14 2010, 11:18PM
I'm not sure if that is sarcasm, Proud Mary, I certainly hope not, as I was just pointing out an error in your calculation. I'm not sure what experience or knowledge has to do with this.
Anders M.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Tue Jun 15 2010, 12:11AM
Very good to know. I was starting to have my doubts about this, but now i am reassured.
I ran into a snag on distance though. My long extension cord is gone, and now i only can find my 100' one. So i came up with a solution; I'll put myself in the basement. The rays would have to go through a whole bunch of earth, and then some cinder block and a lead apron to reach me.
Also, i'm thinking of buying some 1mm lead flashing to line the box, i need it anyway to make an apron. Problem is, it's $125. Maybe if i get this thing running alright, i could start a radiograph service. People could send me an item and $15, then i use $5 to mail it back w/ a pic and keep $10. Idk.
Image, the box isnt drawn to scale. It's only 3 feet high, tube 2.5 ft off ground.
Adam Munich, Tue Jun 15 2010, 12:11AM
Very good to know. I was starting to have my doubts about this, but now i am reassured.
I ran into a snag on distance though. My long extension cord is gone, and now i only can find my 100' one. So i came up with a solution; I'll put myself in the basement. The rays would have to go through a whole bunch of earth, and then some cinder block and a lead apron to reach me.
Also, i'm thinking of buying some 1mm lead flashing to line the box, i need it anyway to make an apron. Problem is, it's $125. Maybe if i get this thing running alright, i could start a radiograph service. People could send me an item and $15, then i use $5 to mail it back w/ a pic and keep $10. Idk.
Image, the box isnt drawn to scale. It's only 3 feet high, tube 2.5 ft off ground.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Tue Jun 15 2010, 02:50AM
I don't know if i want to do this anymore. But i put so much time and money into it. God i wish i could just sell it all and forget about it. I know i'll hate myself for it but it's just not worth it, but i'm afraid of it. I can't afford any lead sheet.
How much could i sell the tube for? It's in great condition. What could i do with the lead box?
I'll keep the transformer and variac, but even then, i have no use.
F*ck i'm just so conflicted right now. I'd hate to sell it, i don't want to spend the $$ to finish it. Please help me decide.
Adam Munich, Tue Jun 15 2010, 02:50AM
I don't know if i want to do this anymore. But i put so much time and money into it. God i wish i could just sell it all and forget about it. I know i'll hate myself for it but it's just not worth it, but i'm afraid of it. I can't afford any lead sheet.
How much could i sell the tube for? It's in great condition. What could i do with the lead box?
I'll keep the transformer and variac, but even then, i have no use.
F*ck i'm just so conflicted right now. I'd hate to sell it, i don't want to spend the $$ to finish it. Please help me decide.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Tue Jun 15 2010, 03:11AM
I'm taking it apart again, this time for good. I'll sell the tube, the holder, the intensifying screens, and the "oil tub" for $200 if anyone is interested. What should i do with the lead box?
Also, what's a good project for me to do with that transformer?
Adam Munich, Tue Jun 15 2010, 03:11AM
I'm taking it apart again, this time for good. I'll sell the tube, the holder, the intensifying screens, and the "oil tub" for $200 if anyone is interested. What should i do with the lead box?
Also, what's a good project for me to do with that transformer?
Re: Grenadier's big thread of Röntgen related shenanigans
Proud Mary, Tue Jun 15 2010, 08:57AM
Not at all, Anders. All of my tubes have Be windows, and I didn't stop to think that this dental tube does not when making my calculation. I have no experience at all of using dental tubes, (preferring grounded anode types designed for a few watts input,) but I understand that you do, hence my recommendation.
Proud Mary, Tue Jun 15 2010, 08:57AM
Anders M. wrote ...
I'm not sure if that is sarcasm, Proud Mary, I certainly hope not, as I was just pointing out an error in your calculation. I'm not sure what experience or knowledge has to do with this.
I'm not sure if that is sarcasm, Proud Mary, I certainly hope not, as I was just pointing out an error in your calculation. I'm not sure what experience or knowledge has to do with this.
Not at all, Anders. All of my tubes have Be windows, and I didn't stop to think that this dental tube does not when making my calculation. I have no experience at all of using dental tubes, (preferring grounded anode types designed for a few watts input,) but I understand that you do, hence my recommendation.
Re: Grenadier's big thread of Röntgen related shenanigans
Wolfram, Tue Jun 15 2010, 10:45AM
Oh, ok, I misread it then. Sorry for any confusion.
Grenadier, I'm sorry to hear that you've abandoned the project. X-rays can be a very rewarding hobby, and I'm sure you could do it in a safe way, seeing all the safety precautions you've taken.
Anders M.
Wolfram, Tue Jun 15 2010, 10:45AM
Oh, ok, I misread it then. Sorry for any confusion.
Grenadier, I'm sorry to hear that you've abandoned the project. X-rays can be a very rewarding hobby, and I'm sure you could do it in a safe way, seeing all the safety precautions you've taken.
Anders M.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Tue Jun 15 2010, 01:39PM
Well, i'm not so sure anymore i just don't want to spend another $125. I'm going to have to think about this.
Edit: {'m going to leave the tube on ebay for a while for $200. If it sells, project's over. If not, then i'll finish.
Adam Munich, Tue Jun 15 2010, 01:39PM
Anders M. wrote ...
Oh, ok, I misread it then. Sorry for any confusion.
Grenadier, I'm sorry to hear that you've abandoned the project. X-rays can be a very rewarding hobby, and I'm sure you could do it in a safe way, seeing all the safety precautions you've taken.
Oh, ok, I misread it then. Sorry for any confusion.
Grenadier, I'm sorry to hear that you've abandoned the project. X-rays can be a very rewarding hobby, and I'm sure you could do it in a safe way, seeing all the safety precautions you've taken.
Well, i'm not so sure anymore i just don't want to spend another $125. I'm going to have to think about this.
Edit: {'m going to leave the tube on ebay for a while for $200. If it sells, project's over. If not, then i'll finish.
Re: Grenadier's big thread of Röntgen related shenanigans
Wolfram, Tue Jun 15 2010, 01:57PM
What will cost you 125$?
Anders M.
Wolfram, Tue Jun 15 2010, 01:57PM
What will cost you 125$?
Anders M.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Tue Jun 15 2010, 02:42PM
Lead sheet to make an apron. I'm just starting to doubt whether this is worth it. I already spent 300 making it, and i just don't think it's worth it. I'll just take a few pics and probably get bored with it. Idk, i'll wait a week to see if the tube will sell. What's a good project to use that transformer for?
Edit; i decided not to quit. I just have to figure out where i can get the money to buy a roll of lead flashing. I only need 8 sq feet to make an apron, so with the rest, i''m going to just line the back of the box (side facing me) a bunch of times to reduce my doserate to zero. The beam side will be fcing away from me, so that doesn't need "reinforcing".
I'm just tring to figure out what i can sell for $$$. What i have lined up so far are a
ti83 calculator,
60gb ipod hard drive
Basic stamp sx
an eeepc with a broken lcd
2 160gb laptop hard drives (sata)
I'm still thinking of stuff.
Also, i've noticed that rad pro calc goes up at from .1mr/h at 5mmPb to .4mr/h at 6mm, down to .02mr/h at 7mm. I'm starting to doubt this calculator. (there's no E-x)
Adam Munich, Tue Jun 15 2010, 02:42PM
Anders M. wrote ...
What will cost you 125$?
Anders M.
What will cost you 125$?
Anders M.
Lead sheet to make an apron. I'm just starting to doubt whether this is worth it. I already spent 300 making it, and i just don't think it's worth it. I'll just take a few pics and probably get bored with it. Idk, i'll wait a week to see if the tube will sell. What's a good project to use that transformer for?
Edit; i decided not to quit. I just have to figure out where i can get the money to buy a roll of lead flashing. I only need 8 sq feet to make an apron, so with the rest, i''m going to just line the back of the box (side facing me) a bunch of times to reduce my doserate to zero. The beam side will be fcing away from me, so that doesn't need "reinforcing".
I'm just tring to figure out what i can sell for $$$. What i have lined up so far are a
ti83 calculator,
60gb ipod hard drive
Basic stamp sx
an eeepc with a broken lcd
2 160gb laptop hard drives (sata)
I'm still thinking of stuff.
Also, i've noticed that rad pro calc goes up at from .1mr/h at 5mmPb to .4mr/h at 6mm, down to .02mr/h at 7mm. I'm starting to doubt this calculator. (there's no E-x)
Re: Grenadier's big thread of Röntgen related shenanigans
klugesmith, Tue Jun 15 2010, 03:55PM
Please please please don't give up for lack of a lead apron.
With your heavy lead box, remote control, dose rate analysis, and invitations for review...
your concern for radiation safety is better than that of most amateur radiographers found here & on the internet.
I think a quantitative dosimeter would serve you better (and more cheaply) than a lead apron.
Could send you a low-range (200 mR which is about 2 mSv) pen dosimeter, but can't spare the charger for it.
With your extreme shielding, a plain Geiger counter could be useful.
Be sure it works, such as by running it close to x-ray source at very low currents.
Then if it indicates NO activity where you stand to operate the xray system,
that will confirm the calculation of negligible exposure.
klugesmith, Tue Jun 15 2010, 03:55PM
Please please please don't give up for lack of a lead apron.
With your heavy lead box, remote control, dose rate analysis, and invitations for review...
your concern for radiation safety is better than that of most amateur radiographers found here & on the internet.
I think a quantitative dosimeter would serve you better (and more cheaply) than a lead apron.
Could send you a low-range (200 mR which is about 2 mSv) pen dosimeter, but can't spare the charger for it.
With your extreme shielding, a plain Geiger counter could be useful.
Be sure it works, such as by running it close to x-ray source at very low currents.
Then if it indicates NO activity where you stand to operate the xray system,
that will confirm the calculation of negligible exposure.
Re: Grenadier's big thread of Röntgen related shenanigans
Wolfram, Tue Jun 15 2010, 04:28PM
Yeah, I also got some strange results from it.
If we can't trust that calculator, how can we then figure out the received dose for a given amount of shielding? One idea could be to use quoted dose rates for dental x-rays at known tube voltages, currents, distances and inherent filtration, and then add in factors like the known half-value layer of lead at the given tube voltage and the inverse-square law.
An other option might be to actually measure it, but then one would need some clever way to do this without having to buy very expensive equipment. Proud Mary, are there any viable ways to do this? Normal GM tubes are obviously out, as their sensitivity at lower energies is very uneven. Ionization chambers might work, and are simple to make, but I remember Uzzors had some trouble with the one he made not working properly. Special geiger tubes made for measuring x-rays might also be an alternative, if the energy response is relatively flat down to 25keV, and if they are easy to get, but I doubt this. Lastly, there are quartz-fiber dosimeters made for low dose rates, but they are not that common, and I don't know how good they are at lower energies. How about scintillation counters?
I won't tell you to ditch any safety measures, but I did some quick, back-of-the-envelope calculations, and I think the dose rate 400' away, with the lead box, will be so low that you won't even be able to measure it with the tube running at 50kV. At 70kV, it might be measurable with a very sensitive instrument. At this range, the radiation will be several times below background, and any advantage of the lead apron will be negated many times over by the lead you will be exposed to when making the apron. Radiation exposure is no joke, but neither is lead exposure, and if you were to take as thorough precautions when working with lead as you do with this project, you would have to be hundreds of feet away even before thinking about melting it.
Anders M.
Wolfram, Tue Jun 15 2010, 04:28PM
Yeah, I also got some strange results from it.
If we can't trust that calculator, how can we then figure out the received dose for a given amount of shielding? One idea could be to use quoted dose rates for dental x-rays at known tube voltages, currents, distances and inherent filtration, and then add in factors like the known half-value layer of lead at the given tube voltage and the inverse-square law.
An other option might be to actually measure it, but then one would need some clever way to do this without having to buy very expensive equipment. Proud Mary, are there any viable ways to do this? Normal GM tubes are obviously out, as their sensitivity at lower energies is very uneven. Ionization chambers might work, and are simple to make, but I remember Uzzors had some trouble with the one he made not working properly. Special geiger tubes made for measuring x-rays might also be an alternative, if the energy response is relatively flat down to 25keV, and if they are easy to get, but I doubt this. Lastly, there are quartz-fiber dosimeters made for low dose rates, but they are not that common, and I don't know how good they are at lower energies. How about scintillation counters?
I won't tell you to ditch any safety measures, but I did some quick, back-of-the-envelope calculations, and I think the dose rate 400' away, with the lead box, will be so low that you won't even be able to measure it with the tube running at 50kV. At 70kV, it might be measurable with a very sensitive instrument. At this range, the radiation will be several times below background, and any advantage of the lead apron will be negated many times over by the lead you will be exposed to when making the apron. Radiation exposure is no joke, but neither is lead exposure, and if you were to take as thorough precautions when working with lead as you do with this project, you would have to be hundreds of feet away even before thinking about melting it.
Anders M.
Re: Grenadier's big thread of Röntgen related shenanigans
Proud Mary, Tue Jun 15 2010, 05:55PM
With a parallel plate ionisation chamber, one can calculate from first principles, as was done in olden times. 1 Röntgen is that quantity of radiation needed to liberate positive and negative charges of one electrostatic unit of charge in 1 cc of dry air - which represents about 2.08 × 10E9 ion pairs.
Dosimetry using silicon PIN photodiodes can also be worked up from first principles as described with formulae in 'Silicon PIN Diode Radiation Detectors' here:
There are plenty of costly radiation detecting PIN diodes made by Hammamatsu and so on, but if we go back twenty years we find that inexpensive types such as BPX65 were used in dosimetry, as described in US patent 5055691 here:
GM tubes are not at all suitable for measuring X-rays, though most, but not all, will detect their presence if the rays are energetic enough to pass through the tube wall and knock some electrons out of it.
This energy response curve is typical of GM tubes generally, though some are better, and some are worse. Filters of tin, brass, bismuth and so on, are sometimes wrapped round the outside of the tube to improve the energy response across certain parts of the spectrum.
Special X-ray sensitive GM tubes were produced until about 1960, but are no longer available. They differed to ordinary GM tubes in operating at a much higher gas pressure to increase the chance of collisions.
While it is possible to calibrate from first principles, as I have said, in practice calibration is usually performed by reference to certified secondary standards, themselves derived from primary national or international standards.
Proud Mary, Tue Jun 15 2010, 05:55PM
Anders M. wrote ...
An other option might be to actually measure it, but then one would need some clever way to do this without having to buy very expensive equipment. Proud Mary, are there any viable ways to do this? Normal GM tubes are obviously out, as their sensitivity at lower energies is very uneven. Ionization chambers might work, and are simple to make, but I remember Uzzors had some trouble with the one he made not working properly. Special geiger tubes made for measuring x-rays might also be an alternative, if the energy response is relatively flat down to 25keV, and if they are easy to get, but I doubt this. Lastly, there are quartz-fiber dosimeters made for low dose rates, but they are not that common, and I don't know how good they are at lower energies. How about scintillation counters?
An other option might be to actually measure it, but then one would need some clever way to do this without having to buy very expensive equipment. Proud Mary, are there any viable ways to do this? Normal GM tubes are obviously out, as their sensitivity at lower energies is very uneven. Ionization chambers might work, and are simple to make, but I remember Uzzors had some trouble with the one he made not working properly. Special geiger tubes made for measuring x-rays might also be an alternative, if the energy response is relatively flat down to 25keV, and if they are easy to get, but I doubt this. Lastly, there are quartz-fiber dosimeters made for low dose rates, but they are not that common, and I don't know how good they are at lower energies. How about scintillation counters?
With a parallel plate ionisation chamber, one can calculate from first principles, as was done in olden times. 1 Röntgen is that quantity of radiation needed to liberate positive and negative charges of one electrostatic unit of charge in 1 cc of dry air - which represents about 2.08 × 10E9 ion pairs.
Dosimetry using silicon PIN photodiodes can also be worked up from first principles as described with formulae in 'Silicon PIN Diode Radiation Detectors' here:
There are plenty of costly radiation detecting PIN diodes made by Hammamatsu and so on, but if we go back twenty years we find that inexpensive types such as BPX65 were used in dosimetry, as described in US patent 5055691 here:
GM tubes are not at all suitable for measuring X-rays, though most, but not all, will detect their presence if the rays are energetic enough to pass through the tube wall and knock some electrons out of it.
This energy response curve is typical of GM tubes generally, though some are better, and some are worse. Filters of tin, brass, bismuth and so on, are sometimes wrapped round the outside of the tube to improve the energy response across certain parts of the spectrum.
Special X-ray sensitive GM tubes were produced until about 1960, but are no longer available. They differed to ordinary GM tubes in operating at a much higher gas pressure to increase the chance of collisions.
While it is possible to calibrate from first principles, as I have said, in practice calibration is usually performed by reference to certified secondary standards, themselves derived from primary national or international standards.
Re: Grenadier's big thread of Röntgen related shenanigans
Proud Mary, Tue Jun 15 2010, 06:00PM
Proud Mary, Tue Jun 15 2010, 06:00PM
Proud Mary wrote ...
With a parallel plate ionisation chamber, one can calculate from first principles, as was done in olden times. 1 Röntgen is that quantity of radiation needed to liberate positive and negative charges of one electrostatic unit of charge in 1 cc of dry air - which represents about 2.08 × 10E9 ion pairs.
Dosimetry using silicon PIN photodiodes can also be worked up from first principles as described with formulae in 'Silicon PIN Diode Radiation Detectors' here:
There are plenty of costly radiation detecting PIN diodes made by Hammamatsu and so on, but if we go back twenty years we find that inexpensive types such as BPX65 were used in dosimetry, as described in US patent 5055691 here:
GM tubes are not at all suitable for measuring X-rays, though most, but not all, will detect their presence if the rays are energetic enough to pass through the tube wall and knock some electrons out of it.
This energy response curve is typical of GM tubes generally, though some are better, and some are worse. Filters of tin, brass, bismuth and so on, are sometimes wrapped round the outside of the tube to improve the energy response across certain parts of the spectrum.
Special X-ray sensitive GM tubes were produced until about 1960, but are no longer available. They differed to ordinary GM tubes in operating at a much higher gas pressure to increase the chance of collisions.
While it is possible to calibrate from first principles, as I have said, in practice calibration is usually performed by reference to certified secondary standards, which are themselves derived from primary national, or international standards.
Anders M. wrote ...
An other option might be to actually measure it, but then one would need some clever way to do this without having to buy very expensive equipment. Proud Mary, are there any viable ways to do this? Normal GM tubes are obviously out, as their sensitivity at lower energies is very uneven. Ionization chambers might work, and are simple to make, but I remember Uzzors had some trouble with the one he made not working properly. Special geiger tubes made for measuring x-rays might also be an alternative, if the energy response is relatively flat down to 25keV, and if they are easy to get, but I doubt this. Lastly, there are quartz-fiber dosimeters made for low dose rates, but they are not that common, and I don't know how good they are at lower energies. How about scintillation counters?
An other option might be to actually measure it, but then one would need some clever way to do this without having to buy very expensive equipment. Proud Mary, are there any viable ways to do this? Normal GM tubes are obviously out, as their sensitivity at lower energies is very uneven. Ionization chambers might work, and are simple to make, but I remember Uzzors had some trouble with the one he made not working properly. Special geiger tubes made for measuring x-rays might also be an alternative, if the energy response is relatively flat down to 25keV, and if they are easy to get, but I doubt this. Lastly, there are quartz-fiber dosimeters made for low dose rates, but they are not that common, and I don't know how good they are at lower energies. How about scintillation counters?
With a parallel plate ionisation chamber, one can calculate from first principles, as was done in olden times. 1 Röntgen is that quantity of radiation needed to liberate positive and negative charges of one electrostatic unit of charge in 1 cc of dry air - which represents about 2.08 × 10E9 ion pairs.
Dosimetry using silicon PIN photodiodes can also be worked up from first principles as described with formulae in 'Silicon PIN Diode Radiation Detectors' here:
There are plenty of costly radiation detecting PIN diodes made by Hammamatsu and so on, but if we go back twenty years we find that inexpensive types such as BPX65 were used in dosimetry, as described in US patent 5055691 here:
GM tubes are not at all suitable for measuring X-rays, though most, but not all, will detect their presence if the rays are energetic enough to pass through the tube wall and knock some electrons out of it.
This energy response curve is typical of GM tubes generally, though some are better, and some are worse. Filters of tin, brass, bismuth and so on, are sometimes wrapped round the outside of the tube to improve the energy response across certain parts of the spectrum.
Special X-ray sensitive GM tubes were produced until about 1960, but are no longer available. They differed to ordinary GM tubes in operating at a much higher gas pressure to increase the chance of collisions.
While it is possible to calibrate from first principles, as I have said, in practice calibration is usually performed by reference to certified secondary standards, which are themselves derived from primary national, or international standards.
Re: Grenadier's big thread of Röntgen related shenanigans
Wolfram, Tue Jun 15 2010, 06:40PM
Thanks, excellent info.
That graph is quite interesting. These tubes would obviously not be very accurate for a quantitive measurement, or for use in high-radiation enviroments, due to the dead time, but when it comes to evaluating if shielding is adequate, the fact that the sensitivity of the tube is rising steeply in the area from 7keV to 70keV might actually be advantageous, as this means that it will "overestimate" the x-ray photons which are most likely to be the ones getting through the shielding.
Just out of interest, which particular tube is this graph for?
Anders M.
Wolfram, Tue Jun 15 2010, 06:40PM
Thanks, excellent info.
That graph is quite interesting. These tubes would obviously not be very accurate for a quantitive measurement, or for use in high-radiation enviroments, due to the dead time, but when it comes to evaluating if shielding is adequate, the fact that the sensitivity of the tube is rising steeply in the area from 7keV to 70keV might actually be advantageous, as this means that it will "overestimate" the x-ray photons which are most likely to be the ones getting through the shielding.
Just out of interest, which particular tube is this graph for?
Anders M.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Tue Jun 15 2010, 07:05PM
Well anders, i can't be 400' away. Only 75. But if you look at the picture i posted, i can be in my basement. The rays would have to pass through 20+' of dirt and some cinder block to get me. But the problem is, i still want an apron. even though i don't think anything will get to me, i'm still paranoid. I really have no idea how much current could go through this tube. But the system, bulb + transformer only draws .8a at 120v (50 on primary coil) with the secondary shorted. This leads me to believe that it can't supply more than 1ma. But i'm not sure. The mA's could easily be much higher, the voltage lower on the secondary.
I just don't think it's worth it... Too many things could go wrong. I'm just going to wait. If my tube sells, that's the end of it. I could just scrap or sell the box, but nobody would want that box, and if they do, nobody would pay to ship it.
What kind of fun could i have with that transformer? Any ideas?
Adam Munich, Tue Jun 15 2010, 07:05PM
Well anders, i can't be 400' away. Only 75. But if you look at the picture i posted, i can be in my basement. The rays would have to pass through 20+' of dirt and some cinder block to get me. But the problem is, i still want an apron. even though i don't think anything will get to me, i'm still paranoid. I really have no idea how much current could go through this tube. But the system, bulb + transformer only draws .8a at 120v (50 on primary coil) with the secondary shorted. This leads me to believe that it can't supply more than 1ma. But i'm not sure. The mA's could easily be much higher, the voltage lower on the secondary.
I just don't think it's worth it... Too many things could go wrong. I'm just going to wait. If my tube sells, that's the end of it. I could just scrap or sell the box, but nobody would want that box, and if they do, nobody would pay to ship it.
What kind of fun could i have with that transformer? Any ideas?
Re: Grenadier's big thread of Röntgen related shenanigans
Proud Mary, Tue Jun 15 2010, 07:35PM
That curve is for Centronic's ZP1401, a mica end-window type, but they all look very much the same, with a rapid ascent to a peak around 60 - 70keV, followed by a fairly steep descent that gradually tapers off.
You'll notice that a small increase in keV can give rise to a large increase in counts, and that there are two points, one on each side of the peak, which will give the same reading despite being far apart on the energy axis. Clearly, a person who is unaware of this gross non-linearity would be seriously misled by an uncompensated GM tube count.
Proud Mary, Tue Jun 15 2010, 07:35PM
Anders M. wrote ...
Just out of interest, which particular tube is this graph for?
Just out of interest, which particular tube is this graph for?
That curve is for Centronic's ZP1401, a mica end-window type, but they all look very much the same, with a rapid ascent to a peak around 60 - 70keV, followed by a fairly steep descent that gradually tapers off.
You'll notice that a small increase in keV can give rise to a large increase in counts, and that there are two points, one on each side of the peak, which will give the same reading despite being far apart on the energy axis. Clearly, a person who is unaware of this gross non-linearity would be seriously misled by an uncompensated GM tube count.
Re: Grenadier's big thread of Röntgen related shenanigans
Wolfram, Tue Jun 15 2010, 08:02PM
And with a lower voltage and a higher current, the radiation dose would be much lower. For any given power, the combination with the highest voltage will always make the largest amount of radiation.
Anders M.
Wolfram, Tue Jun 15 2010, 08:02PM
Grenadier wrote ...
This leads me to believe that it can't supply more than 1ma. But i'm not sure. The mA's could easily be much higher, the voltage lower on the secondary
This leads me to believe that it can't supply more than 1ma. But i'm not sure. The mA's could easily be much higher, the voltage lower on the secondary
And with a lower voltage and a higher current, the radiation dose would be much lower. For any given power, the combination with the highest voltage will always make the largest amount of radiation.
Anders M.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Tue Jun 15 2010, 08:06PM
I don't know. I'll have to think about it for a while.
Do you think that dirt will offer enough protection? It would have to go through 20-30 feet of it.
Edit: I really hope that tube sells. Please help me find someone who will buy it. This whole thing has caused me nothing but grief.
Adam Munich, Tue Jun 15 2010, 08:06PM
I don't know. I'll have to think about it for a while.
Do you think that dirt will offer enough protection? It would have to go through 20-30 feet of it.
Edit: I really hope that tube sells. Please help me find someone who will buy it. This whole thing has caused me nothing but grief.
Re: Grenadier's big thread of Röntgen related shenanigans
Wolfram, Tue Jun 15 2010, 11:59PM
I don't know how well dirt shields radiation, but I would imagine 20-30 feet of it would be very effective in your case.
Anders M.
Wolfram, Tue Jun 15 2010, 11:59PM
I don't know how well dirt shields radiation, but I would imagine 20-30 feet of it would be very effective in your case.
Anders M.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Wed Jun 16 2010, 12:01AM
Nah, i decided i'm done with this. It's caused me too much trouble. Hopefully i can sell the tube.
I'm starting to think about this again, however i still need to make $125.
What is a better ballast idea? I'm stumped.
edit; just tested it with a 120 ohm resistor, transformer draws 1a short circuit, so 1.2ma secondary minimum. Problem is i don't know the voltage. It could very well be 30ma at a low voltage, and that could easily fry the tube...
If i can scrounge up $125, the project is back on, otherwise it's a dud. (the tube's not selling anyway)
edit 2; i'm gonna go for it. I want to be the youngest person to make a fully functional coolidge x-ray machine. that'll look good on a resume. I still need your input on the transformer current/voltage, and what you predict what will happen. Plus i still need $125. If you want to buy anything i listed, (cept the tube), go for it!
I bit the bullet and bought the sheet. Maybe when this is done i can radiograph people's stuff for $8
Final schematic revision.
[Edit: Try not to triple post]
Adam Munich, Wed Jun 16 2010, 12:01AM
Nah, i decided i'm done with this. It's caused me too much trouble. Hopefully i can sell the tube.
I'm starting to think about this again, however i still need to make $125.
What is a better ballast idea? I'm stumped.
edit; just tested it with a 120 ohm resistor, transformer draws 1a short circuit, so 1.2ma secondary minimum. Problem is i don't know the voltage. It could very well be 30ma at a low voltage, and that could easily fry the tube...
If i can scrounge up $125, the project is back on, otherwise it's a dud. (the tube's not selling anyway)
edit 2; i'm gonna go for it. I want to be the youngest person to make a fully functional coolidge x-ray machine. that'll look good on a resume. I still need your input on the transformer current/voltage, and what you predict what will happen. Plus i still need $125. If you want to buy anything i listed, (cept the tube), go for it!
I bit the bullet and bought the sheet. Maybe when this is done i can radiograph people's stuff for $8
Final schematic revision.
[Edit: Try not to triple post]
Re: Grenadier's big thread of Röntgen related shenanigans
Wolfram, Thu Jun 17 2010, 08:17AM
A high current through the tube won't necessarily kill it, it's high current in combination with high voltage thas will kill it, high power in other words. A high current through the transformer secondary is very likely to kill the transformer though. For this reason I would absolutely put a current meter on the secondary side.
I would also place the SSR after the variac. Variacs usually draw a very large current surge at startup, even small ones. Having the SSR switch this current every time you want to do an exposure is not a good idea. It's even worse if the SSR is a zero-crossing one, as the worst possible time to turn a transformer on is at the zero crossing. If you have the SSR after the variac, there is an other advantage too, you can read the actual output voltage of the variac before you press the exposure switch. I would also not put the ampere-meter before the variac, as the surge startup current might kill it.
Regarding the ballast resistor, I don't really like that idea, as it's definitely going to make the whole thing harder to control.
There's also no decoupling capacitors on your AVR. I'm sure you just forgot to draw it, just thought I'd mention it because I've had lots of trouble when trying to drive HD44780-based LCDs without enough decoupling capacitance on the microcontroller, these LCDs seem very sensitive to noise on the power and data lines.
Anders M.
Wolfram, Thu Jun 17 2010, 08:17AM
Grenadier wrote ...
Nah, i decided i'm done with this. It's caused me too much trouble. Hopefully i can sell the tube.
I'm starting to think about this again, however i still need to make $125.
What is a better ballast idea? I'm stumped.
edit; just tested it with a 120 ohm resistor, transformer draws 1a short circuit, so 1.2ma secondary minimum. Problem is i don't know the voltage. It could very well be 30ma at a low voltage, and that could easily fry the tube...
If i can scrounge up $125, the project is back on, otherwise it's a dud. (the tube's not selling anyway)
edit 2; i'm gonna go for it. I want to be the youngest person to make a fully functional coolidge x-ray machine. that'll look good on a resume. I still need your input on the transformer current/voltage, and what you predict what will happen. Plus i still need $125. If you want to buy anything i listed, (cept the tube), go for it!
I bit the bullet and bought the sheet. Maybe when this is done i can radiograph people's stuff for $8
Final schematic revision.
[Edit: Try not to triple post]
Nah, i decided i'm done with this. It's caused me too much trouble. Hopefully i can sell the tube.
I'm starting to think about this again, however i still need to make $125.
What is a better ballast idea? I'm stumped.
edit; just tested it with a 120 ohm resistor, transformer draws 1a short circuit, so 1.2ma secondary minimum. Problem is i don't know the voltage. It could very well be 30ma at a low voltage, and that could easily fry the tube...
If i can scrounge up $125, the project is back on, otherwise it's a dud. (the tube's not selling anyway)
edit 2; i'm gonna go for it. I want to be the youngest person to make a fully functional coolidge x-ray machine. that'll look good on a resume. I still need your input on the transformer current/voltage, and what you predict what will happen. Plus i still need $125. If you want to buy anything i listed, (cept the tube), go for it!
I bit the bullet and bought the sheet. Maybe when this is done i can radiograph people's stuff for $8
Final schematic revision.
[Edit: Try not to triple post]
A high current through the tube won't necessarily kill it, it's high current in combination with high voltage thas will kill it, high power in other words. A high current through the transformer secondary is very likely to kill the transformer though. For this reason I would absolutely put a current meter on the secondary side.
I would also place the SSR after the variac. Variacs usually draw a very large current surge at startup, even small ones. Having the SSR switch this current every time you want to do an exposure is not a good idea. It's even worse if the SSR is a zero-crossing one, as the worst possible time to turn a transformer on is at the zero crossing. If you have the SSR after the variac, there is an other advantage too, you can read the actual output voltage of the variac before you press the exposure switch. I would also not put the ampere-meter before the variac, as the surge startup current might kill it.
Regarding the ballast resistor, I don't really like that idea, as it's definitely going to make the whole thing harder to control.
There's also no decoupling capacitors on your AVR. I'm sure you just forgot to draw it, just thought I'd mention it because I've had lots of trouble when trying to drive HD44780-based LCDs without enough decoupling capacitance on the microcontroller, these LCDs seem very sensitive to noise on the power and data lines.
Anders M.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Wed Oct 13 2010, 08:26PM
I feel I never gave a very good reason for abandoning this project. Well here it is.
I did end up getting this working, but the day after I fell very ill. I attributed it to radiation. I ended up going to quite a few doctors and they couldn't figure out what was wrong. It wasn't until I sold the transformer on fusor that I found out it was just a superbug. Don't remember what it was exactly, but it ruined the project nonetheless. I also destroyed my lead box because it was starting to get stress cracks.
Well now that I'm seeing what Freitsu is doing with the tube I sent him, I got the x-ray itch again. In a few months I plan on buying another x-ray head. (well I'll need someone else to get it, I'm banned from egay).
I plan on putting a lot less work into it this time. This project was too hard to be any fun; it got boring. I have 10sqft of 1mm lead sheet left, so I'm just going to wrap the head in it. I'll build a nice wooden box to hold it in too. At night I'll set it up in my backyard, aperture facing the woods. Then I'll just set up the photograph.
Exposure time will be controlled by me plugging it into my basement outlet via a 100ft extension cord; completely idiot proof and fail safe. Not too many rays are going to get me through the 1" aluminum head + lead ceramic tube covering + 3mm lead + 20 ft packed dirt + cinder block wall.
Edit: Awesome. Atlasfrontiers, the guys I bought the SS.White from no longer sell through ebay. They accept credit cards. :D
Edit2: Wow, they have quite a selection! $95 heads!
Adam Munich, Wed Oct 13 2010, 08:26PM
I feel I never gave a very good reason for abandoning this project. Well here it is.
I did end up getting this working, but the day after I fell very ill. I attributed it to radiation. I ended up going to quite a few doctors and they couldn't figure out what was wrong. It wasn't until I sold the transformer on fusor that I found out it was just a superbug. Don't remember what it was exactly, but it ruined the project nonetheless. I also destroyed my lead box because it was starting to get stress cracks.
Well now that I'm seeing what Freitsu is doing with the tube I sent him, I got the x-ray itch again. In a few months I plan on buying another x-ray head. (well I'll need someone else to get it, I'm banned from egay).
I plan on putting a lot less work into it this time. This project was too hard to be any fun; it got boring. I have 10sqft of 1mm lead sheet left, so I'm just going to wrap the head in it. I'll build a nice wooden box to hold it in too. At night I'll set it up in my backyard, aperture facing the woods. Then I'll just set up the photograph.
Exposure time will be controlled by me plugging it into my basement outlet via a 100ft extension cord; completely idiot proof and fail safe. Not too many rays are going to get me through the 1" aluminum head + lead ceramic tube covering + 3mm lead + 20 ft packed dirt + cinder block wall.
Edit: Awesome. Atlasfrontiers, the guys I bought the SS.White from no longer sell through ebay. They accept credit cards. :D
Edit2: Wow, they have quite a selection! $95 heads!
Re: Grenadier's big thread of Röntgen related shenanigans
Freitsu, Thu Oct 14 2010, 07:33AM
Great to hear you're getting back to this rewarding hobby, Grenadier!
A slight highjack:
This is maybe not the best place to introduce myself but I'll go ahead anyway since I don't find a "Welcome section".
I'm a 28 y/o guy from Finland that likes to "mess" around with h/v and in the last few months x-rays caught my interest so I thought that I would read whatever information I could find online about the subject.
I started to generate x-rays with the 6VS-1 shunt stabiliser that when driven to produce x-rays is an avesome little tube with really tiny focalspot!
Well then, moving on. At last I wanted to try out a real x-ray tube, and somehow I found my way to this forum and read/searched around and then found Grenadiers sale/trade thread, we agreed to make a trade and finally I got my long awaited tube!
Freitsu, Thu Oct 14 2010, 07:33AM
Great to hear you're getting back to this rewarding hobby, Grenadier!
A slight highjack:
This is maybe not the best place to introduce myself but I'll go ahead anyway since I don't find a "Welcome section".
I'm a 28 y/o guy from Finland that likes to "mess" around with h/v and in the last few months x-rays caught my interest so I thought that I would read whatever information I could find online about the subject.
I started to generate x-rays with the 6VS-1 shunt stabiliser that when driven to produce x-rays is an avesome little tube with really tiny focalspot!
Well then, moving on. At last I wanted to try out a real x-ray tube, and somehow I found my way to this forum and read/searched around and then found Grenadiers sale/trade thread, we agreed to make a trade and finally I got my long awaited tube!
Re: Grenadier's big thread of Röntgen related shenanigans
Proud Mary, Thu Oct 14 2010, 08:15AM
Welcome Freitsu!
You will find we have about six other enthusiasts here, with one or two who never think about anything else!
Proud Mary, Thu Oct 14 2010, 08:15AM
Freitsu wrote ...
Great to hear you're getting back to this rewarding hobby, Grenadier!
A slight highjack:
This is maybe not the best place to introduce myself but I'll go ahead anyway since I don't find a "Welcome section".
I'm a 28 y/o guy from Finland that likes to "mess" around with h/v and in the last few months x-rays caught my interest so I thought that I would read whatever information I could find online about the subject.
I started to generate x-rays with the 6VS-1 shunt stabiliser that when driven to produce x-rays is an avesome little tube with really tiny focalspot!
Well then, moving on. At last I wanted to try out a real x-ray tube, and somehow I found my way to this forum and read/searched around and then found Grenadiers sale/trade thread, we agreed to make a trade and finally I got my long awaited tube!
Great to hear you're getting back to this rewarding hobby, Grenadier!
A slight highjack:
This is maybe not the best place to introduce myself but I'll go ahead anyway since I don't find a "Welcome section".
I'm a 28 y/o guy from Finland that likes to "mess" around with h/v and in the last few months x-rays caught my interest so I thought that I would read whatever information I could find online about the subject.
I started to generate x-rays with the 6VS-1 shunt stabiliser that when driven to produce x-rays is an avesome little tube with really tiny focalspot!
Well then, moving on. At last I wanted to try out a real x-ray tube, and somehow I found my way to this forum and read/searched around and then found Grenadiers sale/trade thread, we agreed to make a trade and finally I got my long awaited tube!
Welcome Freitsu!
You will find we have about six other enthusiasts here, with one or two who never think about anything else!
Re: Grenadier's big thread of Röntgen related shenanigans
Freitsu, Thu Oct 14 2010, 09:21AM
Thanks!
I think you can count me in that group that never think about anything else! (well except maybe for some sideprojects, currently it's a scopeclock project) ;)
Freitsu, Thu Oct 14 2010, 09:21AM
Proud Mary wrote ...
Welcome Freitsu!
You will find we have about six other enthusiasts here, with one or two who never think about anything else!
Welcome Freitsu!
You will find we have about six other enthusiasts here, with one or two who never think about anything else!
Thanks!
I think you can count me in that group that never think about anything else! (well except maybe for some sideprojects, currently it's a scopeclock project) ;)
Re: Grenadier's big thread of Röntgen related shenanigans
Proud Mary, Thu Oct 14 2010, 09:31AM
Good man!
Proud Mary, Thu Oct 14 2010, 09:31AM
Freitsu wrote ...
Thanks!
I think you can count me in that group that never think about anything else! (well except maybe for some sideprojects, currently it's a scopeclock project) ;)
Proud Mary wrote ...
Welcome Freitsu!
You will find we have about six other enthusiasts here, with one or two who never think about anything else!
Welcome Freitsu!
You will find we have about six other enthusiasts here, with one or two who never think about anything else!
Thanks!
I think you can count me in that group that never think about anything else! (well except maybe for some sideprojects, currently it's a scopeclock project) ;)
Good man!
Re: Grenadier's big thread of Röntgen related shenanigans
Weazel, Sat Oct 16 2010, 06:49AM
if u need a hand not speanding ur money i can help eg go get dud car batterys theres free lead etc
Weazel, Sat Oct 16 2010, 06:49AM
if u need a hand not speanding ur money i can help eg go get dud car batterys theres free lead etc
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Sat Oct 16 2010, 07:03AM
Wouldn't worry about that... I have lead coming out the wazoo ATM.
Adam Munich, Sat Oct 16 2010, 07:03AM
Wouldn't worry about that... I have lead coming out the wazoo ATM.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Wed Oct 20 2010, 05:20AM
Hmm... I like the idea of an x-ray "gun". Simply put it outside and aim it 'twords the woods, place an object + cassette in front, adjust a variac for kVp, flip the filament battery switch, then go in the basement and plug it in (150ft extension cord). Unplug when exposure is done. This way you can take as big a picture as you want, size is only limited by your cassette size.
I could cast a small lead box ~ 5x5x6 in, half inch thick to put the tube in. Drill a hole in it for the aperture, then silicone a piece of glass or maybe thin aluminum over the aperture. Build a wooden holder for tube and put it inside, then fill with oil. Put a lead lid on and boom, directional source. There won't be any direct radiation anywhere but the aperture (.5inch lead for christ's sake). I'll still want to get away though since compton scattering would scatter some rays.
I'm thinking of portability. Maybe I could even make it battery powered with a ZVS, CW multiplier, and some lithium cells. Ignition coil maybe? Battery powered 30kVp x-ray source for taking radiographs of flowers in the woods? :D
Just carry around a backpack of loaded cassettes. If I make the "tube box" a separate entity from the HV power source, it could weigh a manageable 30lbs. Box would be very easy to make, since it's small a plaster of paris mold could be made for it. It should take maybe only 5 tries to get right. Since I'm not using the Pb sheet, that could be used as a lead apron when there is no basement to hide in.
edit: Half inch may be a little excessive. 1cm would do the trick. Plus the tube will have that lead ceramic covering. It's not like I'm going to be anywhere within 100 feet of this while it's on.
Adam Munich, Wed Oct 20 2010, 05:20AM
Hmm... I like the idea of an x-ray "gun". Simply put it outside and aim it 'twords the woods, place an object + cassette in front, adjust a variac for kVp, flip the filament battery switch, then go in the basement and plug it in (150ft extension cord). Unplug when exposure is done. This way you can take as big a picture as you want, size is only limited by your cassette size.
I could cast a small lead box ~ 5x5x6 in, half inch thick to put the tube in. Drill a hole in it for the aperture, then silicone a piece of glass or maybe thin aluminum over the aperture. Build a wooden holder for tube and put it inside, then fill with oil. Put a lead lid on and boom, directional source. There won't be any direct radiation anywhere but the aperture (.5inch lead for christ's sake). I'll still want to get away though since compton scattering would scatter some rays.
I'm thinking of portability. Maybe I could even make it battery powered with a ZVS, CW multiplier, and some lithium cells. Ignition coil maybe? Battery powered 30kVp x-ray source for taking radiographs of flowers in the woods? :D
Just carry around a backpack of loaded cassettes. If I make the "tube box" a separate entity from the HV power source, it could weigh a manageable 30lbs. Box would be very easy to make, since it's small a plaster of paris mold could be made for it. It should take maybe only 5 tries to get right. Since I'm not using the Pb sheet, that could be used as a lead apron when there is no basement to hide in.
edit: Half inch may be a little excessive. 1cm would do the trick. Plus the tube will have that lead ceramic covering. It's not like I'm going to be anywhere within 100 feet of this while it's on.
Re: Grenadier's big thread of Röntgen related shenanigans
Proud Mary, Wed Oct 20 2010, 01:26PM
If you know the size of your focal spot, you can calculate the width of the unsharp image margin at any given distance by simple geometry.
Moreover, you are very likely to run into reciprocity law failure quite quickly as you extend the distance from tube to screen, see:
Seelentag WW, Panzer W, Reciprocity law failure with film/screen combinations for mammography British Journal of Radiology (1978) 51, 529-531
This excerpt was created in the absence of an abstract.
In radiology the validity of the reciprocity law is usually assumed: the film density for a given X-ray spectrum depends only on the tube exposure (the mAs), and not on the exposure time. This reciprocity law holds for non-screen films (Morgan, 1944). For screen/film combinations, where most of the film density is due to exposure to light from the screen, reciprocity law failure may occur. However, for materials used nowadays in general radiology the effect is negligible for exposure times from 0.005 to 1 second. During the course of measurements on film/screen combinations used in mammography, exposure times of up to 20 minutes had to be used (Panzer, et al., 1978). Therefore reciprocity law failure of these materials had to be investigated. It was found that even at an exposure time of 5 seconds the system speed is reduced by some 30% due to reciprocity law failure.
Reciprocity law failure is described in many textbooks, e.g. by Mees and James (1962) and Herz (1969). Photographic emulsions are most sensitive when the intensity of the exposing radiation is such that an exposure time between 0.01 and 10 seconds is required to produce a medium film density.
Proud Mary, Wed Oct 20 2010, 01:26PM
Grenadier wrote ...
you can take as big a picture as you want, size is only limited by your cassette size.
you can take as big a picture as you want, size is only limited by your cassette size.
If you know the size of your focal spot, you can calculate the width of the unsharp image margin at any given distance by simple geometry.
Moreover, you are very likely to run into reciprocity law failure quite quickly as you extend the distance from tube to screen, see:
Seelentag WW, Panzer W, Reciprocity law failure with film/screen combinations for mammography British Journal of Radiology (1978) 51, 529-531
This excerpt was created in the absence of an abstract.
In radiology the validity of the reciprocity law is usually assumed: the film density for a given X-ray spectrum depends only on the tube exposure (the mAs), and not on the exposure time. This reciprocity law holds for non-screen films (Morgan, 1944). For screen/film combinations, where most of the film density is due to exposure to light from the screen, reciprocity law failure may occur. However, for materials used nowadays in general radiology the effect is negligible for exposure times from 0.005 to 1 second. During the course of measurements on film/screen combinations used in mammography, exposure times of up to 20 minutes had to be used (Panzer, et al., 1978). Therefore reciprocity law failure of these materials had to be investigated. It was found that even at an exposure time of 5 seconds the system speed is reduced by some 30% due to reciprocity law failure.
Reciprocity law failure is described in many textbooks, e.g. by Mees and James (1962) and Herz (1969). Photographic emulsions are most sensitive when the intensity of the exposing radiation is such that an exposure time between 0.01 and 10 seconds is required to produce a medium film density.
Re: Grenadier's big thread of Röntgen related shenanigans
klugesmith, Wed Oct 20 2010, 01:55PM
and by how many seconds you can have the HV on before the anode focal spot get hot enough to emit electrons, or the whole anode gets hot enough to crack the glass seal, or (less likely) the XRT overheats somewhere. Oil immersion would help to cool the tube.
In regular service, dental tubeheads don't run for more than 1 second of any minute.
klugesmith, Wed Oct 20 2010, 01:55PM
Grenadier wrote ...
...This way you can take as big a picture as you want, size is only limited by your cassette size.
...This way you can take as big a picture as you want, size is only limited by your cassette size.
and by how many seconds you can have the HV on before the anode focal spot get hot enough to emit electrons, or the whole anode gets hot enough to crack the glass seal, or (less likely) the XRT overheats somewhere. Oil immersion would help to cool the tube.
In regular service, dental tubeheads don't run for more than 1 second of any minute.
Re: Grenadier's big thread of Röntgen related shenanigans
Proud Mary, Wed Oct 20 2010, 02:39PM
At the risk of stating the obvious, the problems of both reciprocity law failure, and anode over-heating with prolonged exposure, will be amplified with distance due to the inverse square law, thus:
Proud Mary, Wed Oct 20 2010, 02:39PM
At the risk of stating the obvious, the problems of both reciprocity law failure, and anode over-heating with prolonged exposure, will be amplified with distance due to the inverse square law, thus:
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Wed Oct 20 2010, 08:20PM
The tube will be oil immersed, that's why I said silicone-sealed aperture. I'm likely going to use oilve oil for the tube because it has a relatively high specific heat (1.97kJ/kg K). I'm going to put the x-former in vegetable oil mainly because vegetable oil is a lot cheaper. And yes, I'll have to spend an hour massaging all the bubbles out of the paper windings. As for overheating + Reciprocity law failure, multiple short exposures solve the problem. On the "mains end" (basement where I will be) I was thinking of an arduino controlling a SSR. For exposures longer than 1.5 seconds the arduino could break up the exposure giving time for heat to dissipate, as well as time for the cassette to "reset". The subjects won't be alive, so there's no need to worry that things will move.
I was also thinking of making the tube part separate, and having two power supplies. One with the giant x-former that plugs into the mains, and the other a flyback + CW generator for portable use.
For the mains transformer I could use ether a resistor on the primary or secondary side to limit the tube current to 750uA. At that current the heat will have time to dissipate. With the low current of a CW I need not worry about current when I use one.
The hardest part will be casting such a large amount of lead. Plaster of paris would likely be the best bet, and I'll have to heat the lead to about 900*F and pour it all once to prevent things from pre-solidifying. I'm only going to use 1cm because I did the math, and assuming a generous 3000 milliseiverts/hour of 75kVp off axis radiation, 10mm would reduce it to 0.376mSv/hr, or nearly nothing at all. Keep in mind this is directly in front of the shield, not 100 feet away. The overall dose of a 10 second exposure at 100 feet would be the same as me living for about a 15 seconds. This does not take into account compton scattering and reflection though, so it's still best to take cover in a basement or behind a car/big tree (for portable use).
Adam Munich, Wed Oct 20 2010, 08:20PM
The tube will be oil immersed, that's why I said silicone-sealed aperture. I'm likely going to use oilve oil for the tube because it has a relatively high specific heat (1.97kJ/kg K). I'm going to put the x-former in vegetable oil mainly because vegetable oil is a lot cheaper. And yes, I'll have to spend an hour massaging all the bubbles out of the paper windings. As for overheating + Reciprocity law failure, multiple short exposures solve the problem. On the "mains end" (basement where I will be) I was thinking of an arduino controlling a SSR. For exposures longer than 1.5 seconds the arduino could break up the exposure giving time for heat to dissipate, as well as time for the cassette to "reset". The subjects won't be alive, so there's no need to worry that things will move.
I was also thinking of making the tube part separate, and having two power supplies. One with the giant x-former that plugs into the mains, and the other a flyback + CW generator for portable use.
For the mains transformer I could use ether a resistor on the primary or secondary side to limit the tube current to 750uA. At that current the heat will have time to dissipate. With the low current of a CW I need not worry about current when I use one.
The hardest part will be casting such a large amount of lead. Plaster of paris would likely be the best bet, and I'll have to heat the lead to about 900*F and pour it all once to prevent things from pre-solidifying. I'm only going to use 1cm because I did the math, and assuming a generous 3000 milliseiverts/hour of 75kVp off axis radiation, 10mm would reduce it to 0.376mSv/hr, or nearly nothing at all. Keep in mind this is directly in front of the shield, not 100 feet away. The overall dose of a 10 second exposure at 100 feet would be the same as me living for about a 15 seconds. This does not take into account compton scattering and reflection though, so it's still best to take cover in a basement or behind a car/big tree (for portable use).
Re: Grenadier's big thread of Röntgen related shenanigans
Wolfram, Thu Oct 21 2010, 07:49AM
To safely work with x-rays requires a good understanding of the risks. It seems you don't really understand the risks that well, you over-estimate them greatly.
Why is this a problem? Well, it becomes a problem when you take other unnecessary risks to avoid imagined risks. Like when you give yourself lead poisoning because you wanted to reduce the radiation dose from negligible to unmeasurable.
Think about this. The tube you are using is a dental one. Dentists use these tubes many times a day, and their x-ray rooms are not shielded by 10mm of lead, and the operators are not 100 feet away. X-ray rooms are usually shielded with a couple of millimeters of lead (reference: , first page, also see the very relevant table on page 5), and the operators are only a few feet away from the tube.
Sure, it would be an excellent idea if you already had a 10mm wall thickness lead box, but I can imagine making one would lead to quite a bit of lead exposure (unless you somehow manage to do it from 100 feet away in a completely sealed room), and that's going to do significantly more harm to you than an almost immeasurable quantity of extra x-rays.
Also, aren't you buying a complete x-ray head? In that case, the simplest solution is just to use it as it is, no need to worry about air bubbles getting into the transformer windings, oil leaks, etc.
Anders M.
Wolfram, Thu Oct 21 2010, 07:49AM
To safely work with x-rays requires a good understanding of the risks. It seems you don't really understand the risks that well, you over-estimate them greatly.
Why is this a problem? Well, it becomes a problem when you take other unnecessary risks to avoid imagined risks. Like when you give yourself lead poisoning because you wanted to reduce the radiation dose from negligible to unmeasurable.
Think about this. The tube you are using is a dental one. Dentists use these tubes many times a day, and their x-ray rooms are not shielded by 10mm of lead, and the operators are not 100 feet away. X-ray rooms are usually shielded with a couple of millimeters of lead (reference:
, first page, also see the very relevant table on page 5), and the operators are only a few feet away from the tube.Sure, it would be an excellent idea if you already had a 10mm wall thickness lead box, but I can imagine making one would lead to quite a bit of lead exposure (unless you somehow manage to do it from 100 feet away in a completely sealed room), and that's going to do significantly more harm to you than an almost immeasurable quantity of extra x-rays.
Also, aren't you buying a complete x-ray head? In that case, the simplest solution is just to use it as it is, no need to worry about air bubbles getting into the transformer windings, oil leaks, etc.
Anders M.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Thu Oct 21 2010, 10:43AM
Well I know I'm overestimating the risks, but my philosophy is "better safe than sorry". I still want the lead box so I don't need to wear an apron. I'm not going to get exposed to too much Pb because unlike my other adventure hammering welding and melting that huge box together, this one will just be cast as a single piece. Of course it'll be done outside with a breeze to get rid of fumes. I'll spend all of ten minutes pouring the stuff, and likely the hardest part would be making a suitable mold. The only material I have to work with is plaster of paris. Irregardless, the exposure would be nearly non-significant; less than a plumber making a lead drain pipe.
Once the box is done, it'll be drilled, not too hard. Then It'll be filled with oil + tube and a lid made. Then somehow I'll seal the lid to the box, likely with silicone. The whole thing will be put in a bigger box, so I'll never need to see it again.
The reason I'm taking apart the head is because I want to have the kVp adjustable. The problem with leaving it together and just using a variac is that if I use a variac, the heater voltage would vary too. If I want 40kVp rays the heater would nearly be cold. Plus I'd like to put at least some craftsmanship into this.
Adam Munich, Thu Oct 21 2010, 10:43AM
Well I know I'm overestimating the risks, but my philosophy is "better safe than sorry". I still want the lead box so I don't need to wear an apron. I'm not going to get exposed to too much Pb because unlike my other adventure hammering welding and melting that huge box together, this one will just be cast as a single piece. Of course it'll be done outside with a breeze to get rid of fumes. I'll spend all of ten minutes pouring the stuff, and likely the hardest part would be making a suitable mold. The only material I have to work with is plaster of paris. Irregardless, the exposure would be nearly non-significant; less than a plumber making a lead drain pipe.
Once the box is done, it'll be drilled, not too hard. Then It'll be filled with oil + tube and a lid made. Then somehow I'll seal the lid to the box, likely with silicone. The whole thing will be put in a bigger box, so I'll never need to see it again.
The reason I'm taking apart the head is because I want to have the kVp adjustable. The problem with leaving it together and just using a variac is that if I use a variac, the heater voltage would vary too. If I want 40kVp rays the heater would nearly be cold. Plus I'd like to put at least some craftsmanship into this.
Re: Grenadier's big thread of Röntgen related shenanigans
Proud Mary, Thu Oct 21 2010, 03:38PM
I think it important to understand the basic physics of radiological protection, and what is considered to be best practice in your jurisdiction, and then apply those principles to your own endeavours.
There is no longer believed to be any 'safe' minimum dose, as there was claimed to be in the bad heyday of atmospheric testing. The ALARA principle - As Low As Reasonably Achievable - is a good benchmark to work by.
Of course, lawyers and ambulance chasers can argue themselves a living out of what 'Reasonably' means in ALARA, but I would say that it meant that no radiation should be detectable above background outside the master enclosure of the X-ray system - be that master enclosure a lead box the size of a house brick, or a lead-lined room.
Proud Mary, Thu Oct 21 2010, 03:38PM
I think it important to understand the basic physics of radiological protection, and what is considered to be best practice in your jurisdiction, and then apply those principles to your own endeavours.
There is no longer believed to be any 'safe' minimum dose, as there was claimed to be in the bad heyday of atmospheric testing. The ALARA principle - As Low As Reasonably Achievable - is a good benchmark to work by.
Of course, lawyers and ambulance chasers can argue themselves a living out of what 'Reasonably' means in ALARA, but I would say that it meant that no radiation should be detectable above background outside the master enclosure of the X-ray system - be that master enclosure a lead box the size of a house brick, or a lead-lined room.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Thu Oct 21 2010, 08:18PM
Well before I do anything, I'll need a new radiation detector. I still have that 700V end window probe, but I have no way to use it. I'll need a 700V geiger circuit (audio only, no need for a meter). Any ideas?
Adam Munich, Thu Oct 21 2010, 08:18PM
Well before I do anything, I'll need a new radiation detector. I still have that 700V end window probe, but I have no way to use it. I'll need a 700V geiger circuit (audio only, no need for a meter). Any ideas?
Re: Grenadier's big thread of Röntgen related shenanigans
Proud Mary, Thu Oct 21 2010, 09:34PM
GM tubes are not a suitable means of measuring X-rays.
The graph below shows the energy response curve of a typical GM tube. You'll see that it charges uphill in a breathless rush until it gets to 60keV, and then slides down again, so beyond this peak the count rate goes down while the photon energy goes up! Moreover, there are two points, one on either side of the peak, where X-ray photons of widely different energies will give the same number of counts.
Now as a rule of thumb, two thirds of the emitted photons will be in the lower third of the energy spectrum. For example, if you had 75kVp on your target, then two thirds of the output photons will have an energy of less than 25keV, much of which will be blocked by a GM tube outer wall, or lack the energy to knock electrons out of the cathode, to cause ionization, and the Townsend avalanche which causes a click.
You also have to consider dead time compensation, - compensation for the fact that the tube cannot detect particles in the recovery time following each Townsend avalanche, even though more radiation continues to arrive - always an issue with GM tubes.
A GM counter can usually - but not always - detect the presence of X-rays above a certain minimum photon energy - but it cannot measure them.
More suitable means include ionization chambers, scintillation counters with NaI(Tl) or CsI(Na) or BGO etc, and PIN photodiodes.
Proud Mary, Thu Oct 21 2010, 09:34PM
Grenadier wrote ...
Well before I do anything, I'll need a new radiation detector. I still have that 700V end window probe, but I have no way to use it. I'll need a 700V geiger circuit (audio only, no need for a meter). Any ideas?
Well before I do anything, I'll need a new radiation detector. I still have that 700V end window probe, but I have no way to use it. I'll need a 700V geiger circuit (audio only, no need for a meter). Any ideas?
GM tubes are not a suitable means of measuring X-rays.
The graph below shows the energy response curve of a typical GM tube. You'll see that it charges uphill in a breathless rush until it gets to 60keV, and then slides down again, so beyond this peak the count rate goes down while the photon energy goes up! Moreover, there are two points, one on either side of the peak, where X-ray photons of widely different energies will give the same number of counts.
Now as a rule of thumb, two thirds of the emitted photons will be in the lower third of the energy spectrum. For example, if you had 75kVp on your target, then two thirds of the output photons will have an energy of less than 25keV, much of which will be blocked by a GM tube outer wall, or lack the energy to knock electrons out of the cathode, to cause ionization, and the Townsend avalanche which causes a click.
You also have to consider dead time compensation, - compensation for the fact that the tube cannot detect particles in the recovery time following each Townsend avalanche, even though more radiation continues to arrive - always an issue with GM tubes.
A GM counter can usually - but not always - detect the presence of X-rays above a certain minimum photon energy - but it cannot measure them.
More suitable means include ionization chambers, scintillation counters with NaI(Tl) or CsI(Na) or BGO etc, and PIN photodiodes.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Fri Oct 22 2010, 05:18AM
I don't need to measure them, just detect their presence. My tube is mica windowed, so things could get in easily. An ionization counter is completely useless at the distances I'll be from the thing, and I sure as hell can't afford a scintillator. I'll just feel safer with that clicking noise. If it speeds up I'll know something's wrong.
Adam Munich, Fri Oct 22 2010, 05:18AM
I don't need to measure them, just detect their presence. My tube is mica windowed, so things could get in easily. An ionization counter is completely useless at the distances I'll be from the thing, and I sure as hell can't afford a scintillator. I'll just feel safer with that clicking noise. If it speeds up I'll know something's wrong.
Re: Grenadier's big thread of Röntgen related shenanigans
Proud Mary, Fri Oct 22 2010, 04:36PM
If there is some reason why you feel you must use a GM tube, then I would suggest one with a bismuth cathode, such as the Victoreen 6306, which has about double the X-ray detection efficiency at 50keV compared with an ordinary Cr/Fe cathode tube liner.
Proud Mary, Fri Oct 22 2010, 04:36PM
If there is some reason why you feel you must use a GM tube, then I would suggest one with a bismuth cathode, such as the Victoreen 6306, which has about double the X-ray detection efficiency at 50keV compared with an ordinary Cr/Fe cathode tube liner.
Re: Grenadier's big thread of Röntgen related shenanigans
plazmatron, Fri Oct 22 2010, 08:18PM
Multiple short exposures, will help with overheating, however, they will work against you as far as reciprocity failure is concerned.
Using an x-ray machine in a public area, is likely to invite trouble. Mine is bolted to my worktop, and I wouldn't dream of running it in the presence of others. That way, any mistakes, are mine, and mine alone.
This has been mentioned a few times on this thread, by a few people. Geiger counters really are wholly unsuitable for this task, and in fact can be dangerously unsuitable.
Not only do they have an atrocious response curve, they can easily be driven to saturation resulting in........ no clicks!
So you could be sitting there getting your last ever tan, and never realize it.
I urge you to sort out some kind of ion chamber detector. I find self reading quartz fiber dosimeters to be relatively inexpensive, and reliable. Try and acquire low range types.
For example I have a 500mRem (5mSv) gamma/xray dosimeter, and a 2mSv Gamma/xray dosimeter (The 2mSv dosimeter has a linear response from 50keV to 3MeV), as well as a bunch of high range dosimeters for beam measurement.
You should have at least two detectors that agree with one another, preferably more. I wear three.
Les
plazmatron, Fri Oct 22 2010, 08:18PM
Grenadier wrote ...
As for overheating + Reciprocity law failure, multiple short exposures solve the problem.
As for overheating + Reciprocity law failure, multiple short exposures solve the problem.
Multiple short exposures, will help with overheating, however, they will work against you as far as reciprocity failure is concerned.
Grenadier wrote ...
..........or behind a car/big tree (for portable use).
..........or behind a car/big tree (for portable use).
Using an x-ray machine in a public area, is likely to invite trouble. Mine is bolted to my worktop, and I wouldn't dream of running it in the presence of others. That way, any mistakes, are mine, and mine alone.
Grenadier wrote ...
I don't need to measure them, just detect their presence. My tube is mica windowed, so things could get in easily. An ionization counter is completely useless at the distances I'll be from the thing, and I sure as hell can't afford a scintillator. I'll just feel safer with that clicking noise. If it speeds up I'll know something's wrong
I don't need to measure them, just detect their presence. My tube is mica windowed, so things could get in easily. An ionization counter is completely useless at the distances I'll be from the thing, and I sure as hell can't afford a scintillator. I'll just feel safer with that clicking noise. If it speeds up I'll know something's wrong
This has been mentioned a few times on this thread, by a few people. Geiger counters really are wholly unsuitable for this task, and in fact can be dangerously unsuitable.
Not only do they have an atrocious response curve, they can easily be driven to saturation resulting in........ no clicks!
So you could be sitting there getting your last ever tan, and never realize it.
I urge you to sort out some kind of ion chamber detector. I find self reading quartz fiber dosimeters to be relatively inexpensive, and reliable. Try and acquire low range types.
For example I have a 500mRem (5mSv) gamma/xray dosimeter, and a 2mSv Gamma/xray dosimeter (The 2mSv dosimeter has a linear response from 50keV to 3MeV), as well as a bunch of high range dosimeters for beam measurement.
You should have at least two detectors that agree with one another, preferably more. I wear three.
Les
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Fri Oct 22 2010, 08:34PM
I was thinking of a dosimeter, but my problem is they're only sold on egay and I can't buy things on there anymore. Though it would solve the problem to get one + a charger, I am stuck with a gieger counter. However, if anyone wants to trade me a low range dosimeter + charger for my geiger probe, be my guest.
As for you're public area concern, the only ones in any danger are a few squirrels, and possibly the occasional mouse.
Adam Munich, Fri Oct 22 2010, 08:34PM
I was thinking of a dosimeter, but my problem is they're only sold on egay and I can't buy things on there anymore. Though it would solve the problem to get one + a charger, I am stuck with a gieger counter. However, if anyone wants to trade me a low range dosimeter + charger for my geiger probe, be my guest.
As for you're public area concern, the only ones in any danger are a few squirrels, and possibly the occasional mouse.
Re: Grenadier's big thread of Röntgen related shenanigans
Proud Mary, Sat Oct 23 2010, 12:15AM
To the best of my knowledge, the last dedicated X-ray GM tube , the Centronics ZP1600, has been out of production for some time, and at any rate is no longer in the current Centronics GM Tube Selection Guide.
ZP1600 was designed to detect X-rays from 6 - 20keV, and so was filled with argon (and the usual halogen quench gas) at about 60% of atmospheric pressure to increase the probability of collisions. These so-called 'high pressure' tubes require much higher working voltages than ordinary GM tubes - 1.6kV in the case of ZP1600.
LND still have a rough equivalent to ZP1600 in their list - LND 72219 - for which you should expect to pay $350 or so. The 77219 data sheet is here:
Note how long the Minimum Dead Time is: 100μs
Proud Mary, Sat Oct 23 2010, 12:15AM
To the best of my knowledge, the last dedicated X-ray GM tube , the Centronics ZP1600, has been out of production for some time, and at any rate is no longer in the current Centronics GM Tube Selection Guide.
ZP1600 was designed to detect X-rays from 6 - 20keV, and so was filled with argon (and the usual halogen quench gas) at about 60% of atmospheric pressure to increase the probability of collisions. These so-called 'high pressure' tubes require much higher working voltages than ordinary GM tubes - 1.6kV in the case of ZP1600.
LND still have a rough equivalent to ZP1600 in their list - LND 72219 - for which you should expect to pay $350 or so. The 77219 data sheet is here:
Note how long the Minimum Dead Time is: 100μs
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Sat Oct 23 2010, 04:46AM
I'm going to take your advice and go with the dosimeters then, but how will I acquire them?
Also, please help me pick a head. Which one do you think is good? Whomever's interested Please PM me for the link because lots of people read this forum and I don't want them to get all snatched up.
Adam Munich, Sat Oct 23 2010, 04:46AM
I'm going to take your advice and go with the dosimeters then, but how will I acquire them?
Also, please help me pick a head. Which one do you think is good? Whomever's interested Please PM me for the link because lots of people read this forum and I don't want them to get all snatched up.
Re: Grenadier's big thread of Röntgen related shenanigans
Proud Mary, Sat Oct 23 2010, 09:19PM
Here are the two types of personal dosimeter that I use:
There are deliberately no user controls, and no on/off switch, though the older red Gammatell II unit does have a pressel switch to light the red LED display. Batteries typically last about a year of continuous use at lower exposure rates. Obviously if it is bleeping all the time, battery life will be that much shortened.
The alarm level options are set by a jumper wire, as shown on the card in the yellow unit. Both types use ZP1300 series compensated GM tubes. The DC/DC 450V converter module is the black cast resin block next to the battery in both cases.
Both types are still in use in the UK, though the older Gammatell II with its LED display has been largely displaced by the newer LED type, and the snazzy all-singing all-dancing Siemens EPD Mk 2, which takes X-ray dosimetry down to the 15keV level, and is marketed under the Thermo brand.
All my dosimeters are made in the UK, but US made units will be very similar in form and function.
Proud Mary, Sat Oct 23 2010, 09:19PM
Here are the two types of personal dosimeter that I use:
There are deliberately no user controls, and no on/off switch, though the older red Gammatell II unit does have a pressel switch to light the red LED display. Batteries typically last about a year of continuous use at lower exposure rates. Obviously if it is bleeping all the time, battery life will be that much shortened.
The alarm level options are set by a jumper wire, as shown on the card in the yellow unit. Both types use ZP1300 series compensated GM tubes. The DC/DC 450V converter module is the black cast resin block next to the battery in both cases.
Both types are still in use in the UK, though the older Gammatell II with its LED display has been largely displaced by the newer LED type, and the snazzy all-singing all-dancing Siemens EPD Mk 2, which takes X-ray dosimetry down to the 15keV level, and is marketed under the Thermo brand.
All my dosimeters are made in the UK, but US made units will be very similar in form and function.
Re: Grenadier's big thread of Röntgen related shenanigans
klugesmith, Sun Oct 24 2010, 03:25AM
Here is a picture of a CDV-138 in action:
[edit] and here is one low-range quartz fiber dosimeter on ebay right now:
klugesmith, Sun Oct 24 2010, 03:25AM
Grenadier wrote ...
I was thinking of a dosimeter, but my problem is they're only sold on egay and I can't buy things on there anymore. ...
As for you're public area concern, the only ones in any danger are a few squirrels, and possibly the occasional mouse.
If you wait for a low-range (200 mR) training dosimeter "CDV-138" to be offered on ebay, I would be glad to bid on your behalf. Even have it shipped directly to you. I have a few of my own, from ebay 1 year ago, but not quite ready to part with any of them. The chargers are ubiquitous -- same as the ones used with "standard" CDV dosimeters.I was thinking of a dosimeter, but my problem is they're only sold on egay and I can't buy things on there anymore. ...
As for you're public area concern, the only ones in any danger are a few squirrels, and possibly the occasional mouse.
Here is a picture of a CDV-138 in action:
[edit] and here is one low-range quartz fiber dosimeter on ebay right now:
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Sun Oct 24 2010, 11:54PM
The CDV-138 is perfect for my purposes, as I'm not stupid enough to stand in the beam path. I found one for $7, and a charger for $17. How will this work kludge? Should I just send you money, or would you accept a trade for something I have?
Adam Munich, Sun Oct 24 2010, 11:54PM
The CDV-138 is perfect for my purposes, as I'm not stupid enough to stand in the beam path. I found one for $7, and a charger for $17. How will this work kludge? Should I just send you money, or would you accept a trade for something I have?
Re: Grenadier's big thread of Röntgen related shenanigans
Proud Mary, Mon Oct 25 2010, 01:17PM
The 200mR FSD of the antique CDV-138 QFD is roughly equivalent to 1.75mSv - about 8% of the UK HSE annual adult occupational dose limit of 20mSv.
I see from the Oak Ridge Universities site that these were manufactured between 1956 and 1974.
The seller's enlarged photo shows significant corrosion, so let's hope their keeping qualities are better than they look!
Proud Mary, Mon Oct 25 2010, 01:17PM
The 200mR FSD of the antique CDV-138 QFD is roughly equivalent to 1.75mSv - about 8% of the UK HSE annual adult occupational dose limit of 20mSv.
I see from the Oak Ridge Universities site that these were manufactured between 1956 and 1974.
The seller's enlarged photo shows significant corrosion, so let's hope their keeping qualities are better than they look!
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Mon Oct 25 2010, 08:35PM
Autodesk drawings are done for the head module. You can DL them here.
Box is 3/4" wood with a hinge top, 10" square. I'll put a handle and locking snap on it too. Inside is the lead box, which is 20 cm wide, 12cm long, 16cm tall. I don't think I'll cast it all as one anymore, because things will likely go wrong somehow. Instead I'll cast plates and solder them together with plumbing solder + a pencil torch. Lead sheet will cover the edges since they'll be weak spots. There's a small piece of glass siliconed over the aperture hole, and the pb lid will be siliconed on too. It'll be filled with some sort of oil.
On back there's a 5 ohm rheostat and a switch. The switch turns on the filament and the 5 ohm rheostat will adjust the filament current. (with the HV removed of course) one can see the glow through the aperture to make sure things are OK. Power is supplied by two D cells. I'm going to design a little shutter to cover the aperature in case the glow causes a problem. I haven't designed the HV feedthroughs yet, but I'll likely just use park plugs. Since the tube has quite a low resistance I don't think insulation breakdown will be too much of a problem.
I've decided to build the tube module before I buy the x-ray head so I have an option to give up if things go awry.
Adam Munich, Mon Oct 25 2010, 08:35PM
Autodesk drawings are done for the head module. You can DL them here.
Box is 3/4" wood with a hinge top, 10" square. I'll put a handle and locking snap on it too. Inside is the lead box, which is 20 cm wide, 12cm long, 16cm tall. I don't think I'll cast it all as one anymore, because things will likely go wrong somehow. Instead I'll cast plates and solder them together with plumbing solder + a pencil torch. Lead sheet will cover the edges since they'll be weak spots. There's a small piece of glass siliconed over the aperture hole, and the pb lid will be siliconed on too. It'll be filled with some sort of oil.
On back there's a 5 ohm rheostat and a switch. The switch turns on the filament and the 5 ohm rheostat will adjust the filament current. (with the HV removed of course) one can see the glow through the aperture to make sure things are OK. Power is supplied by two D cells. I'm going to design a little shutter to cover the aperature in case the glow causes a problem. I haven't designed the HV feedthroughs yet, but I'll likely just use park plugs. Since the tube has quite a low resistance I don't think insulation breakdown will be too much of a problem.
I've decided to build the tube module before I buy the x-ray head so I have an option to give up if things go awry.
Re: Grenadier's big thread of Röntgen related shenanigans
uzzors2k, Wed Oct 27 2010, 01:00PM
Hey Grenadier, wait on buying from this guy I purchased one as soon as I saw the link, forgetting to check his feedback. I haven't gotten any response from him yet, nor did the last guy. He's probably forgotten about the auction. 
uzzors2k, Wed Oct 27 2010, 01:00PM
Hey Grenadier, wait on buying from this guy
I purchased one as soon as I saw the link, forgetting to check his feedback. I haven't gotten any response from him yet, nor did the last guy. He's probably forgotten about the auction. Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Wed Oct 27 2010, 07:34PM
Okay. Besides, I'm going to build all the hardware before I mess with the electronics, let alone radiation. I plan on making plaster molds for the lead slabs today. They should be completely dry by friday then.
With the current size of the Pb box, it weighs 30 kg! I may use either 8mm lead or shrink the box a little.
Adam Munich, Wed Oct 27 2010, 07:34PM
Okay. Besides, I'm going to build all the hardware before I mess with the electronics, let alone radiation. I plan on making plaster molds for the lead slabs today. They should be completely dry by friday then.
With the current size of the Pb box, it weighs 30 kg! I may use either 8mm lead or shrink the box a little.
Re: Grenadier's big thread of Röntgen related shenanigans
klugesmith, Fri Oct 29 2010, 07:15PM
4mm of Pb would attenuate 60 keV monochromatic radiation by 8,000,000,000 (lin atten 57 cm^-1)
and 80 keV monochromatic radiation by 50,000 (lin atten 27 cm^-1).
As you know, the x-ray spectrum from a Coolidge tube peaks at a small fraction of the peak kV,
even running on DC (and lower still, running self rectified).
If you can come up with a dosimeter charger, I will give you a tested CDV-138 dosimeter.
Yesterday at the dentist (for a wisdom tooth extraction
), the good fellow was happy to zap
a couple of the dosimeters with a normal diagnostic exposure. They registered 10 and 11 mR,
or roughly 0.1 mSv -- the dose to about 1 cubic inch of your body when your tooth is x-rayed.
A whole-body exposure at that level, repeated daily, would be way over the safety limits.
[edit] There is a standard way to compute the full-body equivalent dose when only part of the body is exposed.
Not simply proportional to exposed volume or mass, it accounts for the relative sensitivity of different tissues.
There's a table of organs and weighting factors which add up to 100% of the body.
I think the gonads get about 20% of the total, which is disproportionate even in my case.
klugesmith, Fri Oct 29 2010, 07:15PM
Grenadier wrote ...
With the current size of the Pb box, it weighs 30 kg! I may use either 8mm lead or shrink the box a little.
You are wasting lead and fuel to melt it.With the current size of the Pb box, it weighs 30 kg! I may use either 8mm lead or shrink the box a little.
4mm of Pb would attenuate 60 keV monochromatic radiation by 8,000,000,000 (lin atten 57 cm^-1)
and 80 keV monochromatic radiation by 50,000 (lin atten 27 cm^-1).
As you know, the x-ray spectrum from a Coolidge tube peaks at a small fraction of the peak kV,
even running on DC (and lower still, running self rectified).
If you can come up with a dosimeter charger, I will give you a tested CDV-138 dosimeter.
Yesterday at the dentist (for a wisdom tooth extraction
), the good fellow was happy to zapa couple of the dosimeters with a normal diagnostic exposure. They registered 10 and 11 mR,
or roughly 0.1 mSv -- the dose to about 1 cubic inch of your body when your tooth is x-rayed.
A whole-body exposure at that level, repeated daily, would be way over the safety limits.
[edit] There is a standard way to compute the full-body equivalent dose when only part of the body is exposed.
Not simply proportional to exposed volume or mass, it accounts for the relative sensitivity of different tissues.
There's a table of organs and weighting factors which add up to 100% of the body.
I think the gonads get about 20% of the total, which is disproportionate even in my case.
Re: Grenadier's big thread of Röntgen related shenanigans
Proud Mary, Sat Oct 30 2010, 12:28PM
It can be handy in the long run to have a good stock of kilogram lead ingots, so you can build shields to suit a particular experiment.
Proud Mary, Sat Oct 30 2010, 12:28PM
It can be handy in the long run to have a good stock of kilogram lead ingots, so you can build shields to suit a particular experiment.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Sat Oct 30 2010, 08:17PM
Alright, enough procrastination, I've started to build the box. I decided on these dimensions: 14cm * 20cm* 11cm with 6mm thick walls. That makes the box a manageable 20lbs, yet still provides adequate protection.
I decided to use plasticine clay to make a positive and use plaster to make a negative. Instead of using words, I decided to use pictures for this part of the build.
Rolling out the clay. (1cm thick guide sticks)
Clay's all rolled nicely.
It's like silly putty!
Making the template.
(20x14)
Cutting the clay to size.
That'll do just nicely.
Plaster time!
A minor inconvenience.
Clay placed in pan.
And plaster poured in pan. I had to use half the carton. I also realized just now it'll be tough to get out of there, but it's set now so I can't move it anyway. I'll get it out somehow.
I'm probably going to need another carton of plaster, but other than that things are going good.
Kludge, I'd love to take you up on that offer. However I won't need it for maybe a month because I want to build all the hardware before I mess with the electronics. As for your numbers, that's the exposure directly in front of the tube, and I'll be far from the aperture when this thing is on.
And proud mary I have 120lbs of lead muffins. I'd say that's a good stock. They aren't really good for stacking though, maybe sometime I'll turn them into bricks.
Adam Munich, Sat Oct 30 2010, 08:17PM
Alright, enough procrastination, I've started to build the box. I decided on these dimensions: 14cm * 20cm* 11cm with 6mm thick walls. That makes the box a manageable 20lbs, yet still provides adequate protection.
I decided to use plasticine clay to make a positive and use plaster to make a negative. Instead of using words, I decided to use pictures for this part of the build.
Rolling out the clay. (1cm thick guide sticks)
Clay's all rolled nicely.
It's like silly putty!
Making the template.
(20x14)
Cutting the clay to size.
That'll do just nicely.
Plaster time!
A minor inconvenience.
Clay placed in pan.
And plaster poured in pan. I had to use half the carton. I also realized just now it'll be tough to get out of there, but it's set now so I can't move it anyway. I'll get it out somehow.
I'm probably going to need another carton of plaster, but other than that things are going good.
Kludge, I'd love to take you up on that offer. However I won't need it for maybe a month because I want to build all the hardware before I mess with the electronics. As for your numbers, that's the exposure directly in front of the tube, and I'll be far from the aperture when this thing is on.
And proud mary I have 120lbs of lead muffins. I'd say that's a good stock. They aren't really good for stacking though, maybe sometime I'll turn them into bricks.
Re: Grenadier's big thread of Röntgen related shenanigans
Bored Chemist, Sun Oct 31 2010, 02:18PM
I still have a scar on my hand from pouring molten lead into a plaster mould.
The hot lead boils the water trapped in the plaster and the steam spatters the molten metal.
Bored Chemist, Sun Oct 31 2010, 02:18PM
I still have a scar on my hand from pouring molten lead into a plaster mould.
The hot lead boils the water trapped in the plaster and the steam spatters the molten metal.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Sun Oct 31 2010, 02:26PM
I learned that the hard way before too. That's why you're supposed to let it dry out for a few days. I plan on leaving it in front of my fireplace for a while, that should get all that water out.
Adam Munich, Sun Oct 31 2010, 02:26PM
I learned that the hard way before too. That's why you're supposed to let it dry out for a few days. I plan on leaving it in front of my fireplace for a while, that should get all that water out.
Re: Grenadier's big thread of Röntgen related shenanigans
Arcstarter, Wed Nov 03 2010, 01:49AM
I have been thinking about buying a lead ingot and casting a few sheets for X-ray shielding. But, it costs 16 dollars for one ingot, so i will have to use some steel as shielding as well. But ill need like 4 times as much of that
Arcstarter, Wed Nov 03 2010, 01:49AM
I have been thinking about buying a lead ingot and casting a few sheets for X-ray shielding. But, it costs 16 dollars for one ingot, so i will have to use some steel as shielding as well. But ill need like 4 times as much of that
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Wed Nov 03 2010, 02:06AM
Two words; Wheel weights. I got about 100lbs of free lead just by asking the auto shops around here. It's 4% antimony so it's quite hard, but still pourable.
Just plop them all in a big pot and put it on a propane burner set to medium. Since most of the weights will be covered in plastic, it will smoke something mean. Cover the pot. After about two hours everything will be melted and the smoke will die down, then you can pour it into muffin tins. I have a box of 120 lead mini-muffins next to my TV, and it's likely going to stay there (heavy!)
Adam Munich, Wed Nov 03 2010, 02:06AM
Two words; Wheel weights. I got about 100lbs of free lead just by asking the auto shops around here. It's 4% antimony so it's quite hard, but still pourable.
Just plop them all in a big pot and put it on a propane burner set to medium. Since most of the weights will be covered in plastic, it will smoke something mean. Cover the pot. After about two hours everything will be melted and the smoke will die down, then you can pour it into muffin tins. I have a box of 120 lead mini-muffins next to my TV, and it's likely going to stay there (heavy!)
Re: Grenadier's big thread of Röntgen related shenanigans
Proud Mary, Wed Nov 03 2010, 10:44AM
I've found the Medi-Ray products catalogue inspirational when giving old lead shielding a makeover to get the bright new look of today.
MarShield do a range of custom designs for their lead aprons, so no one need worry about being caught on the hop by shielding colours clashing with a new outfit:
Proud Mary, Wed Nov 03 2010, 10:44AM
I've found the Medi-Ray products catalogue inspirational when giving old lead shielding a makeover to get the bright new look of today.
MarShield do a range of custom designs for their lead aprons, so no one need worry about being caught on the hop by shielding colours clashing with a new outfit:
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Thu Nov 04 2010, 03:44AM
Alright another update. Things are taking a little longer then expected because I only have enough clay to make one side at a time. I also got distracted with carbon arc lamps.
I've decided to take pictures of every step and make a stop motion build video at the end. Kind of like this. (I'd give anything for that helmet)
All hardened.
Came out pretty easily.
Good thing I used clay.
Uh oh, too wet.
This should fix that.
And it did.
More template cutting.
Perfect!
More clay rolling.
Cut cut.
Decided to not waste so much plaster this time.
All dry.
Came out very easily.
Too wet...
Not too big of a problem.
I should start casting lead by Saturday. I also looked at that medi-ray stuff, and I had no idea lead could be machined so nicely. Too bad I don't have a CNC or a lathe.
Adam Munich, Thu Nov 04 2010, 03:44AM
Alright another update. Things are taking a little longer then expected because I only have enough clay to make one side at a time. I also got distracted with carbon arc lamps.
I've decided to take pictures of every step and make a stop motion build video at the end. Kind of like this. (I'd give anything for that helmet)
All hardened.
Came out pretty easily.
Good thing I used clay.
Uh oh, too wet.
This should fix that.
And it did.
More template cutting.
Perfect!
More clay rolling.
Cut cut.
Decided to not waste so much plaster this time.
All dry.
Came out very easily.
Too wet...
Not too big of a problem.
I should start casting lead by Saturday. I also looked at that medi-ray stuff, and I had no idea lead could be machined so nicely. Too bad I don't have a CNC or a lathe.
Re: Grenadier's big thread of Röntgen related shenanigans
Proud Mary, Thu Nov 04 2010, 11:29AM
If you can find two cheap stainless steel kitchen food containers/canisters, one of which nests inside the other, you can use them to cast very good cylinders - as one needs with transmission target tubes, both for shielding and as an oil cooling jacket. Securing the smaller container inside the larger with steel standoffs, or bolts, you can pour in the molten lead and leave it to solidify without having to extract it from a mold. The outer stainless steel canister makes an excellent surface for dayglo orange epoxy enamel, and seals the lead securely from contact and interaction with the environment.
If the design is well thought through, the original screws or bolts used to hold the canisters apart can also be used to mount the cylinder. These also help to stop the lead rattling loose, as there is a small shrinkage as the Pb changes phase.
As a note of caution, some stainless steel food canisters also contain plastics, and these are useless for our purpose.
Lead shot and casting resins can also be used to mold bespoke shielding parts with an excellent finish and professional appearance.
I am presently working up the design of my first X-ray spectrometer, and will start a projects thread about it in the next few weeks, so interested parties will be able to see my shielding methods for themselves.
Proud Mary, Thu Nov 04 2010, 11:29AM
Grenadier wrote ...
I also looked at that medi-ray stuff, and I had no idea lead could be machined so nicely. Too bad I don't have a CNC or a lathe.
I also looked at that medi-ray stuff, and I had no idea lead could be machined so nicely. Too bad I don't have a CNC or a lathe.
If you can find two cheap stainless steel kitchen food containers/canisters, one of which nests inside the other, you can use them to cast very good cylinders - as one needs with transmission target tubes, both for shielding and as an oil cooling jacket. Securing the smaller container inside the larger with steel standoffs, or bolts, you can pour in the molten lead and leave it to solidify without having to extract it from a mold. The outer stainless steel canister makes an excellent surface for dayglo orange epoxy enamel, and seals the lead securely from contact and interaction with the environment.
If the design is well thought through, the original screws or bolts used to hold the canisters apart can also be used to mount the cylinder. These also help to stop the lead rattling loose, as there is a small shrinkage as the Pb changes phase.
As a note of caution, some stainless steel food canisters also contain plastics, and these are useless for our purpose.
Lead shot and casting resins can also be used to mold bespoke shielding parts with an excellent finish and professional appearance.
I am presently working up the design of my first X-ray spectrometer, and will start a projects thread about it in the next few weeks, so interested parties will be able to see my shielding methods for themselves.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Thu Nov 04 2010, 07:51PM
That sounds pretty easy to do, but it would be a cylinder, and cylinders make poor use of space inside a square box. I picked a prism because there will be a lot of extra space, and extra space means more oil. More oil means more thermal mass and thus more heat capacity. I might put a thermometer in there too, since I would have no idea how hot things are getting inside.
Since I plan on sealing the lead box I may just use the PCB oil that came with the head. It has a high thermal capacity, a relatively high boiling point compared to vegetable oil smoke points, and it is non-flammable. Not only that, it won't degrade like vegetable oils will. Plus it's light. Wow, I can see why the manufactures loved this stuff.
As for your x-ray spectrometer, how are you going to differentiate between the energies?
Adam Munich, Thu Nov 04 2010, 07:51PM
That sounds pretty easy to do, but it would be a cylinder, and cylinders make poor use of space inside a square box. I picked a prism because there will be a lot of extra space, and extra space means more oil. More oil means more thermal mass and thus more heat capacity. I might put a thermometer in there too, since I would have no idea how hot things are getting inside.
Since I plan on sealing the lead box I may just use the PCB oil that came with the head. It has a high thermal capacity, a relatively high boiling point compared to vegetable oil smoke points, and it is non-flammable. Not only that, it won't degrade like vegetable oils will. Plus it's light. Wow, I can see why the manufactures loved this stuff.
As for your x-ray spectrometer, how are you going to differentiate between the energies?
Re: Grenadier's big thread of Röntgen related shenanigans
Proud Mary, Thu Nov 04 2010, 09:10PM
I've had for some time a range of new sealed proportional counter tubes covering ~1.5keV to 50keV - and the transmission target tubes to match - but my attempts to find a multichannel pulse amplitude analyser at an affordable price had so far met without success.
I was browsing through October's abstracts a few weeks ago, when I chanced upon the following:
Nakaye, Y. Kawai, J. Recording X-ray spectra with an audio digitizer X-Ray Spectrometry, Volume 39, Issue 5, 318–320, September/October 2010
X-ray spectra were recorded with a notebook computer and analyzed by software on the computer, without a pulse height analyzer (PHA) or a digital signal processor (DSP). An audio (microphone or line) input on a personal computer has a built-in analogue-to-digital converter (ADC) for digital audio recording. The output signal of the X-ray detector is recorded through the audio input of the computer and then analyzed by software on the computer. On the basis of this method, X-rays from a radium source were measured with a cadmium telluride detector. K X-rays of bismuth were detected. Full width at half maximum (FWHM) was 5.6 keV at Kα of bismuth (77.1 keV), enough to separate Kβ (87.3 keV) from Kα of bismuth. The present method achieved almost equal energy resolution as that of the regular method (5.3 keV FWHM at 77.1 keV).
I'd been worrying away at a similar solution to the problem for the last year - I'd imagined a V-F converter plugged into the audio card and a waterfall spectrum display - so the Japanese paper confirmed what I already knew: that I had all the parts, tools, and know-how to build an X-ray spectrometer, and that it wouldn't be a dead end project, but would naturally lead on to more experiments and a greater understanding of soft X-rays, where all the exciting research is happening nowadays - in my view at least.
Proud Mary, Thu Nov 04 2010, 09:10PM
Grenadier wrote ...
As for your x-ray spectrometer, how are you going to differentiate between the energies?
As for your x-ray spectrometer, how are you going to differentiate between the energies?
I've had for some time a range of new sealed proportional counter tubes covering ~1.5keV to 50keV - and the transmission target tubes to match - but my attempts to find a multichannel pulse amplitude analyser at an affordable price had so far met without success.
I was browsing through October's abstracts a few weeks ago, when I chanced upon the following:
Nakaye, Y. Kawai, J. Recording X-ray spectra with an audio digitizer X-Ray Spectrometry, Volume 39, Issue 5, 318–320, September/October 2010
X-ray spectra were recorded with a notebook computer and analyzed by software on the computer, without a pulse height analyzer (PHA) or a digital signal processor (DSP). An audio (microphone or line) input on a personal computer has a built-in analogue-to-digital converter (ADC) for digital audio recording. The output signal of the X-ray detector is recorded through the audio input of the computer and then analyzed by software on the computer. On the basis of this method, X-rays from a radium source were measured with a cadmium telluride detector. K X-rays of bismuth were detected. Full width at half maximum (FWHM) was 5.6 keV at Kα of bismuth (77.1 keV), enough to separate Kβ (87.3 keV) from Kα of bismuth. The present method achieved almost equal energy resolution as that of the regular method (5.3 keV FWHM at 77.1 keV).
I'd been worrying away at a similar solution to the problem for the last year - I'd imagined a V-F converter plugged into the audio card and a waterfall spectrum display - so the Japanese paper confirmed what I already knew: that I had all the parts, tools, and know-how to build an X-ray spectrometer, and that it wouldn't be a dead end project, but would naturally lead on to more experiments and a greater understanding of soft X-rays, where all the exciting research is happening nowadays - in my view at least.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Thu Nov 04 2010, 10:41PM
Hmm... What about using an arduino for data logging? At 16 something megahertz the clock is fast enough, and you can use some analog to digital converters to harvest the data. Maxim has a 1wire chip that can harvest four 16 bit analog channels, and if you use ten inputs on an arduino that's 40 channels.
Adam Munich, Thu Nov 04 2010, 10:41PM
Proud Mary wrote ...
but my attempts to find a multichannel pulse amplitude analyser at an affordable price had so far met without success.
but my attempts to find a multichannel pulse amplitude analyser at an affordable price had so far met without success.
Hmm... What about using an arduino for data logging? At 16 something megahertz the clock is fast enough, and you can use some analog to digital converters to harvest the data. Maxim has a 1wire chip that can harvest four 16 bit analog channels, and if you use ten inputs on an arduino that's 40 channels.
Re: Grenadier's big thread of Röntgen related shenanigans
Proud Mary, Thu Nov 04 2010, 11:16PM
Designing and making the spectrometer hardware to a good standard places me already right at the very edge of my modest abilities, so I'll just stick with Nakaye's peer-reviewed paper for the pulse amplitude spectrum analysis for the time being, though I may condition the pulses as a second step once I have some signals to analyse. Anyway, I'll be starting a project thread about it when I can find the time to build and photograph each stage in a way that others might find interesting or helpful.
Proud Mary, Thu Nov 04 2010, 11:16PM
Grenadier wrote ...
Hmm... What about using an arduino for data logging? At 16 something megahertz the clock is fast enough, and you can use some analog to digital converters to harvest the data. Maxim has a 1wire chip that can harvest four 16 bit analog channels, and if you use ten inputs on an arduino that's 40 channels.
Proud Mary wrote ...
but my attempts to find a multichannel pulse amplitude analyser at an affordable price had so far met without success.
but my attempts to find a multichannel pulse amplitude analyser at an affordable price had so far met without success.
Hmm... What about using an arduino for data logging? At 16 something megahertz the clock is fast enough, and you can use some analog to digital converters to harvest the data. Maxim has a 1wire chip that can harvest four 16 bit analog channels, and if you use ten inputs on an arduino that's 40 channels.
Designing and making the spectrometer hardware to a good standard places me already right at the very edge of my modest abilities, so I'll just stick with Nakaye's peer-reviewed paper for the pulse amplitude spectrum analysis for the time being, though I may condition the pulses as a second step once I have some signals to analyse. Anyway, I'll be starting a project thread about it when I can find the time to build and photograph each stage in a way that others might find interesting or helpful.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Fri Nov 12 2010, 06:15AM
Moar progress;
Third mold's done.
Sanding things nice and smooth.
Is it level?
[link]
Mmm... Muffins.
Nothing like some coffee warm things up.
Level things off with some pennies.
Mercury switches make great levels.
Plumbum falls.
Crap I, there is some bubbling and a hairline crack.
I'll have some more lead in my cheese plz.
Bake at 350, maybe this will drive out the water.
Crap II, something broke.
That's nothing a little tape can't fix.
When the lead oxidizes it's ready to pour.
Attempt 5. Yes 5. Turns out the large piece of plaster is really hydroscopic. After 5 pours all the water has been driven out and things work great. This really makes a quick task a long one though.
After that the mold has seen some better days, and has also changed color.
Repeat that 2x.
Visitor.
Casting the 14x11
Casting the 14x20
All the pieces. Due to my poor measurement, they're all around 9mm thick. Oh well, extra protection.
They all line up quite nicely. A few need to be bent a little bit, but soldering shouldn't be very hard to do.
25 lbs.. Not too bad actually.
So next up is soldering. Not sure how I'm going to do that, may have to borrow a 100w solder gun from someone. I'm going to hate to drill an aperature hole in this box, but it'd be useless without one. I also wonder how I'm going to drill a 1.5" hole in hard lead. Maybe I'll have my school's tech dept CNC one.
Since this sheild is really hefty, it should be good all the way up to 120kVp. I have no reason to go that high though.
Adam Munich, Fri Nov 12 2010, 06:15AM
Moar progress;
Third mold's done.
Sanding things nice and smooth.
Is it level?
[link]
Mmm... Muffins.
Nothing like some coffee warm things up.
Level things off with some pennies.
Mercury switches make great levels.
Plumbum falls.
Crap I, there is some bubbling and a hairline crack.
I'll have some more lead in my cheese plz.
Bake at 350, maybe this will drive out the water.
Crap II, something broke.
That's nothing a little tape can't fix.
When the lead oxidizes it's ready to pour.
Attempt 5. Yes 5. Turns out the large piece of plaster is really hydroscopic. After 5 pours all the water has been driven out and things work great. This really makes a quick task a long one though.
After that the mold has seen some better days, and has also changed color.
Repeat that 2x.
Visitor.
Casting the 14x11
Casting the 14x20
All the pieces. Due to my poor measurement, they're all around 9mm thick. Oh well, extra protection.
They all line up quite nicely. A few need to be bent a little bit, but soldering shouldn't be very hard to do.
25 lbs.. Not too bad actually.
So next up is soldering. Not sure how I'm going to do that, may have to borrow a 100w solder gun from someone. I'm going to hate to drill an aperature hole in this box, but it'd be useless without one. I also wonder how I'm going to drill a 1.5" hole in hard lead. Maybe I'll have my school's tech dept CNC one.
Since this sheild is really hefty, it should be good all the way up to 120kVp. I have no reason to go that high though.
Re: Grenadier's big thread of Röntgen related shenanigans
Proud Mary, Fri Nov 12 2010, 08:47AM
You could drill a hole large enough to get a rat's tail needle file in, and then work it up till you can get the next size file in, and/or drill a circle of holes, and join up the dots. Drill very slowly to avoid melting and keep the swarf in spirals.
Some angle irons inside and out would hold those corners nicely, as well as providing sound anchor points for grab handles, or mountings of some kind, and adding a bit more shielding.
Some folks might say you've gone a bit over the top, and could have used less Pb, but not me. It's important for peace of mind to be totally confident in your shielding, and if that means erring on the side of caution, so be it.
Proud Mary, Fri Nov 12 2010, 08:47AM
Grenadier wrote ...
So next up is soldering. Not sure how I'm going to do that, may have to borrow a 100w solder gun from someone. I'm going to have to drill an aperture hole in this box, but it'd be useless without one. I also wonder how I'm going to drill a 1.5" hole in hard lead. Maybe I'll have my school's tech dept CNC one.
So next up is soldering. Not sure how I'm going to do that, may have to borrow a 100w solder gun from someone. I'm going to have to drill an aperture hole in this box, but it'd be useless without one. I also wonder how I'm going to drill a 1.5" hole in hard lead. Maybe I'll have my school's tech dept CNC one.
You could drill a hole large enough to get a rat's tail needle file in, and then work it up till you can get the next size file in, and/or drill a circle of holes, and join up the dots. Drill very slowly to avoid melting and keep the swarf in spirals.
Some angle irons inside and out would hold those corners nicely, as well as providing sound anchor points for grab handles, or mountings of some kind, and adding a bit more shielding.
Some folks might say you've gone a bit over the top, and could have used less Pb, but not me. It's important for peace of mind to be totally confident in your shielding, and if that means erring on the side of caution, so be it.
Re: Grenadier's big thread of Röntgen related shenanigans
uzzors2k, Fri Nov 12 2010, 03:02PM
Impressive shield, Grenadier!
uzzors2k, Fri Nov 12 2010, 03:02PM
Impressive shield, Grenadier!
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Fri Nov 12 2010, 11:29PM
I never thought of using a file, thanks PM. A dremel with a cutoff wheel could work too. I can't cut anything until I solder this box togrther though, and I'll try to get that done next week. But I have a problem... Where will I get some 60/40 plumbing solder? All I can buy now is that crappy lead free stuff.
After I build the lead box, the woodworking will be the biggest job. I have no time to get into my school's woodtech dept though. Maybe before hours I could, provided a teacher would be willing to go to work at 5:30...
Adam Munich, Fri Nov 12 2010, 11:29PM
I never thought of using a file, thanks PM. A dremel with a cutoff wheel could work too. I can't cut anything until I solder this box togrther though, and I'll try to get that done next week. But I have a problem... Where will I get some 60/40 plumbing solder? All I can buy now is that crappy lead free stuff.
After I build the lead box, the woodworking will be the biggest job. I have no time to get into my school's woodtech dept though. Maybe before hours I could, provided a teacher would be willing to go to work at 5:30...
Re: Grenadier's big thread of Röntgen related shenanigans
Proud Mary, Sat Nov 13 2010, 01:41AM
I think you may get into difficulties if you try to solder the corners of your slab cast box. Heat will be conducted away from the joint so fast that I doubt that even a 180W iron as used in stained glass etc would be able to make normal soldering possible. An iron which had the wattage to keep the solder mobile as you moved along the seem would probably start melting big holes in the work. There are folk on this forum that know more about brazing and such than I do, so hopefully one of them would share their thoughts with you. If you are going to use solder, it would be plumber's solder that you should be after, much thicker than the electronics grade.
Beyond using cornerless lead cyclinders as I suggested above, how would I tackle the box problem? Probably with the reinforcing angle irons I suggested above on the outside, and perhaps with lead sheet bonded with epoxy on the inside of the corners.
Proud Mary, Sat Nov 13 2010, 01:41AM
Grenadier wrote ...
I never thought of using a file, thanks PM. A dremel with a cutoff wheel could work too. I can't cut anything until I solder this box togrther though, and I'll try to get that done next week. But I have a problem... Where will I get some 60/40 plumbing solder? All I can buy now is that crappy lead free stuff.
After I build the lead box, the woodworking will be the biggest job. I have no time to get into my school's woodtech dept though. Maybe before hours I could, provided a teacher would be willing to go to work at 5:30...
I never thought of using a file, thanks PM. A dremel with a cutoff wheel could work too. I can't cut anything until I solder this box togrther though, and I'll try to get that done next week. But I have a problem... Where will I get some 60/40 plumbing solder? All I can buy now is that crappy lead free stuff.
After I build the lead box, the woodworking will be the biggest job. I have no time to get into my school's woodtech dept though. Maybe before hours I could, provided a teacher would be willing to go to work at 5:30...
I think you may get into difficulties if you try to solder the corners of your slab cast box. Heat will be conducted away from the joint so fast that I doubt that even a 180W iron as used in stained glass etc would be able to make normal soldering possible. An iron which had the wattage to keep the solder mobile as you moved along the seem would probably start melting big holes in the work. There are folk on this forum that know more about brazing and such than I do, so hopefully one of them would share their thoughts with you. If you are going to use solder, it would be plumber's solder that you should be after, much thicker than the electronics grade.
Beyond using cornerless lead cyclinders as I suggested above, how would I tackle the box problem? Probably with the reinforcing angle irons I suggested above on the outside, and perhaps with lead sheet bonded with epoxy on the inside of the corners.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Sat Nov 13 2010, 02:17AM
Hmm, I think I'll just get a pencil butane torch then. I had one but the butane tank cracked. :( I don't think it would melt holes in these plates, they have quite a lot of thermal mass.
Of course I meant plumbers solder. The problem is I can't buy 60/40 plubers stuff anywhere. There is lead electronics solder here aplenty, but it would take a whole lot of that to weld this together.
I could also just JB weld the hell out of the box too. That stuff is very strong, and oil-proof. Actually I'm going to do that. JB weld or liquid nails would make putting this together very easy and cheap. Then I could use lead sheet on the inside seams to prevent rays from getting out.
Adam Munich, Sat Nov 13 2010, 02:17AM
Hmm, I think I'll just get a pencil butane torch then. I had one but the butane tank cracked. :( I don't think it would melt holes in these plates, they have quite a lot of thermal mass.
Of course I meant plumbers solder. The problem is I can't buy 60/40 plubers stuff anywhere. There is lead electronics solder here aplenty, but it would take a whole lot of that to weld this together.
I could also just JB weld the hell out of the box too. That stuff is very strong, and oil-proof. Actually I'm going to do that. JB weld or liquid nails would make putting this together very easy and cheap. Then I could use lead sheet on the inside seams to prevent rays from getting out.
Re: Grenadier's big thread of Röntgen related shenanigans
Arcstarter, Sat Nov 13 2010, 05:03AM
Well, the solder and like likely melt at the same temperature or thereabouts, so in order to get the solder to melt, the lead would have to be close to the same temperature. The large thermal mass only means that it is that much harder to get the lead up to temperature. Maybe it will work, i have never done such a thing.
Arcstarter, Sat Nov 13 2010, 05:03AM
Well, the solder and like likely melt at the same temperature or thereabouts, so in order to get the solder to melt, the lead would have to be close to the same temperature. The large thermal mass only means that it is that much harder to get the lead up to temperature. Maybe it will work, i have never done such a thing
.Re: Grenadier's big thread of Röntgen related shenanigans
Proud Mary, Sat Nov 13 2010, 12:59PM
I don't know the glues you mention, but will say that surface preparation is everything with adhesives if they are to perform well.
Of course, X-rays can degrade polymers much as solar UV can rot car tyres and discolour plastics in hot countries, but I can't see this being a problem at the doses likely to be absorbed by the adhesive on the reverse side of your lead corner overlays.
I've been trying to learn about the possible production of hazardous organolead compounds that might be liberated by a reaction between the different sorts of resins and lead shot/granules in the making of castable shielding, but as I know even less about chemistry than I do about electricity, I haven't come up with any very reliable-looking conclusions yet. The anti-knocking agent tetraethyl lead is the most famous organolead compound, and there's no keeping company with it, as we all know.
Proud Mary, Sat Nov 13 2010, 12:59PM
Grenadier wrote ...
Hmm, I think I'll just get a pencil butane torch then. I had one but the butane tank cracked. :( I don't think it would melt holes in these plates, they have quite a lot of thermal mass.
Of course I meant plumbers solder. The problem is I can't buy 60/40 plubers stuff anywhere. There is lead electronics solder here aplenty, but it would take a whole lot of that to weld this together.
I could also just JB weld the hell out of the box too. That stuff is very strong, and oil-proof. Actually I'm going to do that. JB weld or liquid nails would make putting this together very easy and cheap. Then I could use lead sheet on the inside seams to prevent rays from getting out.
Hmm, I think I'll just get a pencil butane torch then. I had one but the butane tank cracked. :( I don't think it would melt holes in these plates, they have quite a lot of thermal mass.
Of course I meant plumbers solder. The problem is I can't buy 60/40 plubers stuff anywhere. There is lead electronics solder here aplenty, but it would take a whole lot of that to weld this together.
I could also just JB weld the hell out of the box too. That stuff is very strong, and oil-proof. Actually I'm going to do that. JB weld or liquid nails would make putting this together very easy and cheap. Then I could use lead sheet on the inside seams to prevent rays from getting out.
I don't know the glues you mention, but will say that surface preparation is everything with adhesives if they are to perform well.
Of course, X-rays can degrade polymers much as solar UV can rot car tyres and discolour plastics in hot countries, but I can't see this being a problem at the doses likely to be absorbed by the adhesive on the reverse side of your lead corner overlays.
I've been trying to learn about the possible production of hazardous organolead compounds that might be liberated by a reaction between the different sorts of resins and lead shot/granules in the making of castable shielding, but as I know even less about chemistry than I do about electricity, I haven't come up with any very reliable-looking conclusions yet. The anti-knocking agent tetraethyl lead is the most famous organolead compound, and there's no keeping company with it, as we all know.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Sat Nov 13 2010, 03:12PM
Well JB weld is a two part epoxy, and it's very strong when hardened. It's what I used to put together that light emitting antidiode.
Liquid nails is a cyanocarylate based adhesive, and it's crazy strong when hardened. It's often used in construction now when laying floors and ceiling tiles. Sometimes it's even used to hold down flashing and roofing shingles.
As for surface prep, a dremel + a 60 grit wheel would roughen things up quite nicely.
I would stay away from organolead compounds proud may as they are much more toxic than lead metal itself. Just like methyl mercury is much more toxic than mercury metal.
If you want to make castable sheilding, or even better yet a sheild made of a clay like material, why not try lead powder? It could easily be mixed with plasticine.
Adam Munich, Sat Nov 13 2010, 03:12PM
Well JB weld is a two part epoxy, and it's very strong when hardened. It's what I used to put together that light emitting antidiode.
Liquid nails is a cyanocarylate based adhesive, and it's crazy strong when hardened. It's often used in construction now when laying floors and ceiling tiles. Sometimes it's even used to hold down flashing and roofing shingles.
As for surface prep, a dremel + a 60 grit wheel would roughen things up quite nicely.
I would stay away from organolead compounds proud may as they are much more toxic than lead metal itself. Just like methyl mercury is much more toxic than mercury metal.
If you want to make castable sheilding, or even better yet a sheild made of a clay like material, why not try lead powder? It could easily be mixed with plasticine.
Re: Grenadier's big thread of Röntgen related shenanigans
Proud Mary, Sat Nov 13 2010, 03:51PM
The epoxy sounds right, and the lead internal corners should stiffen the box a bit too. I believe lead can be expected to deform under its own weight over time, so bracing the corners can only help.
As for lead toxicity, I feel confident about working with the metal when wearing gloves, but as you say, the organolead compounds should be avoided at all costs. It's a shame, because the big shielding companies are able to produce a clear water-white acrylic with 30% by weight of lead as a dissolved organolead compound, but there's no way that the little guy could reproduce the safety conditions essential in this kind of chemical process.
That's why I've turned to the idea of castable shielding using lead shot - not my idea, but one that lends itself to low risk small scale production. As a variation on this, I have several low power XRD tubes intended to operate inside an oil cooling jacket, and am looking at the oil flowing through lead shot inside the jacket, which will not only cool the tube, but increase the average density of the lead shot shield.
Proud Mary, Sat Nov 13 2010, 03:51PM
The epoxy sounds right, and the lead internal corners should stiffen the box a bit too. I believe lead can be expected to deform under its own weight over time, so bracing the corners can only help.
As for lead toxicity, I feel confident about working with the metal when wearing gloves, but as you say, the organolead compounds should be avoided at all costs. It's a shame, because the big shielding companies are able to produce a clear water-white acrylic with 30% by weight of lead as a dissolved organolead compound, but there's no way that the little guy could reproduce the safety conditions essential in this kind of chemical process.
That's why I've turned to the idea of castable shielding using lead shot - not my idea, but one that lends itself to low risk small scale production. As a variation on this, I have several low power XRD tubes intended to operate inside an oil cooling jacket, and am looking at the oil flowing through lead shot inside the jacket, which will not only cool the tube, but increase the average density of the lead shot shield.
Re: Grenadier's big thread of Röntgen related shenanigans
klugesmith, Sat Nov 13 2010, 06:26PM
With your open-face mold, consider buoyancy of the core.
Also you can use an ordinary hole saw. Keep it cool with a dribble of water while cutting.
As for joining:
Did you make some spare slabs for bonding practice?
I would put a test bond in a vise and break it on purpose.
Bet that a solder bond would be MUCH stronger and more ductile than JB-weld on a lead surface, however prepared. I think you could do the job with tin/lead solder and a butane torch -- don't forget to use flux. Know your melting points.
Could also assemble the box with screws to carry the load -- then seal the seams with material of your choice.
Will your machine be restricted to horizontal or vertical x-ray beams?
klugesmith, Sat Nov 13 2010, 06:26PM
Grenadier wrote ...
I also wonder how I'm going to drill a 1.5" hole in hard lead. Maybe I'll have my school's tech dept CNC one.
A bit late for this comment, but the easiest way would be to put a 1.5" round core in your mold before the slab is cast! Could be some plaster of Paris hardened in a drinking glass, or a metal pipe or stack of washers that could be knocked out with a hammer, or a tin can full of sand...I also wonder how I'm going to drill a 1.5" hole in hard lead. Maybe I'll have my school's tech dept CNC one.
With your open-face mold, consider buoyancy of the core.
Also you can use an ordinary hole saw. Keep it cool with a dribble of water while cutting.
As for joining:
Did you make some spare slabs for bonding practice?
I would put a test bond in a vise and break it on purpose.
Bet that a solder bond would be MUCH stronger and more ductile than JB-weld on a lead surface, however prepared. I think you could do the job with tin/lead solder and a butane torch -- don't forget to use flux. Know your melting points.
Could also assemble the box with screws to carry the load -- then seal the seams with material of your choice.
Will your machine be restricted to horizontal or vertical x-ray beams?
Re: Grenadier's big thread of Röntgen related shenanigans
Proud Mary, Sat Nov 13 2010, 09:04PM
On reflection, I must say I am inclined to share Klugesmith's scepticism about an entirely glued structure, and will go back to my first suggestion, which was to use angle irons on the corners, inside and out, which is what I would surely do were the problem mine.
Proud Mary, Sat Nov 13 2010, 09:04PM
On reflection, I must say I am inclined to share Klugesmith's scepticism about an entirely glued structure, and will go back to my first suggestion, which was to use angle irons on the corners, inside and out, which is what I would surely do were the problem mine.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Mon Nov 15 2010, 03:38AM
Well it all depends. If I can find some 60/40 plumbing stuff then I'll solder it. If not, I'll use glue.
I'm not going to use angle irons because that would require me to drill a whole bunch of small holes, and that would create even more problems to solve.
Adam Munich, Mon Nov 15 2010, 03:38AM
Well it all depends. If I can find some 60/40 plumbing stuff then I'll solder it. If not, I'll use glue.
I'm not going to use angle irons because that would require me to drill a whole bunch of small holes, and that would create even more problems to solve.
Re: Grenadier's big thread of Röntgen related shenanigans
Steve Conner, Mon Nov 15 2010, 10:13AM
In the olden days, large banks of lead-acid batteries used to get their cells joined together by "lead burning". The battery's own voltage was used to weld the terminals to lead busbars, using a lead stick as the welding rod. Maybe you can weld your lead box together in the same way.
Probably not such a good idea in this era of health and safety, but then neither was casting the lead in the first place.
Steve Conner, Mon Nov 15 2010, 10:13AM
In the olden days, large banks of lead-acid batteries used to get their cells joined together by "lead burning". The battery's own voltage was used to weld the terminals to lead busbars, using a lead stick as the welding rod. Maybe you can weld your lead box together in the same way.
Probably not such a good idea in this era of health and safety, but then neither was casting the lead in the first place.
Re: Grenadier's big thread of Röntgen related shenanigans
Wolfram, Mon Nov 15 2010, 01:24PM
I tried this by accident once and was greeted by a large choking cloud of lead vapor. Not recommended.
Anders M.
Wolfram, Mon Nov 15 2010, 01:24PM
Steve McConner wrote ...
In the olden days, large banks of lead-acid batteries used to get their cells joined together by "lead burning". The battery's own voltage was used to weld the terminals to lead busbars, using a lead stick as the welding rod. Maybe you can weld your lead box together in the same way.
Probably not such a good idea in this era of health and safety, but then neither was casting the lead in the first place.
In the olden days, large banks of lead-acid batteries used to get their cells joined together by "lead burning". The battery's own voltage was used to weld the terminals to lead busbars, using a lead stick as the welding rod. Maybe you can weld your lead box together in the same way.
Probably not such a good idea in this era of health and safety, but then neither was casting the lead in the first place.
I tried this by accident once and was greeted by a large choking cloud of lead vapor. Not recommended.
Anders M.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Mon Nov 15 2010, 08:41PM
I never intended to try that anyway. Sounds like a good way to destroy my plates.
Adam Munich, Mon Nov 15 2010, 08:41PM
I never intended to try that anyway. Sounds like a good way to destroy my plates.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Thu Nov 25 2010, 05:18PM
Well I couldn't find any leaded solder no matter where I looked so I ended up getting a roll of thick rosin cored lead free stuff, only because it melts at 430*F. That gives me about a 120* lee-way before the 5% antimonial lead melts, so if I work slowly and have a wet sponge on hand I should be able to solder it w/o too much damage. I plan on soldering the thing together sometime before monday.
Since it's cold now I'll do the soldering inside.
Adam Munich, Thu Nov 25 2010, 05:18PM
Well I couldn't find any leaded solder no matter where I looked so I ended up getting a roll of thick rosin cored lead free stuff, only because it melts at 430*F. That gives me about a 120* lee-way before the 5% antimonial lead melts, so if I work slowly and have a wet sponge on hand I should be able to solder it w/o too much damage. I plan on soldering the thing together sometime before monday.
Since it's cold now I'll do the soldering inside.
Re: Grenadier's big thread of Röntgen related shenanigans
klugesmith, Thu Nov 25 2010, 07:04PM
Happy Thanksgiving, Adam.
It's cold here too -- buckets of water were frozen over the last couple mornings.
A lesson from welding class:
Consider tack-soldering all 8 corners of your box before doing any of the long joints.
(or put it together with a few temporary screws, or many angle brackets & clamps).
1) keeps the whole thing square from the outset.
2) otherwise if you start at one end of a long joint, thermal expansion/contraction may cause it to develop an unwanted gap or skew before you get to the other end.
By coincidence, speaking of shielding boxes, I'm about to find out if 5/8" drywall (gypsum board) can practically block x-rays at NST voltage (15 kV RMS). If so, then I'll make a box out of that, this weekend, and play at the limited voltage before getting out the lead and the oil.
klugesmith, Thu Nov 25 2010, 07:04PM
Happy Thanksgiving, Adam.
It's cold here too -- buckets of water were frozen over the last couple mornings.
A lesson from welding class:
Consider tack-soldering all 8 corners of your box before doing any of the long joints.
(or put it together with a few temporary screws, or many angle brackets & clamps).
1) keeps the whole thing square from the outset.
2) otherwise if you start at one end of a long joint, thermal expansion/contraction may cause it to develop an unwanted gap or skew before you get to the other end.
By coincidence, speaking of shielding boxes, I'm about to find out if 5/8" drywall (gypsum board) can practically block x-rays at NST voltage (15 kV RMS). If so, then I'll make a box out of that, this weekend, and play at the limited voltage before getting out the lead and the oil.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Thu Nov 25 2010, 07:24PM
Yeah I was planning on soldering the corners before anything else. I still haven't decided If I want to solder things from the inside or outside though.
As for staying square, all the sides line up perfectly so I don' think it'll be too hard to do. It's kind of like putting those little birdhouse kits together; everything just fits.
As for your drywall discovery, that's pretty interesting. Y'know what you can do for short experiments is mix lead shot with plaster of paris. That would make castable, yet brittle and clunky shielding. It'd be good for short experiments though. The best part about it is that you can get your lead shit back by simply dissolving the plaster in HCl. Lead reacts very slowly with acid but the gypsum would dissolve away in only a few minutes.
Adam Munich, Thu Nov 25 2010, 07:24PM
Yeah I was planning on soldering the corners before anything else. I still haven't decided If I want to solder things from the inside or outside though.
As for staying square, all the sides line up perfectly so I don' think it'll be too hard to do. It's kind of like putting those little birdhouse kits together; everything just fits.
As for your drywall discovery, that's pretty interesting. Y'know what you can do for short experiments is mix lead shot with plaster of paris. That would make castable, yet brittle and clunky shielding. It'd be good for short experiments though. The best part about it is that you can get your lead shit back by simply dissolving the plaster in HCl. Lead reacts very slowly with acid but the gypsum would dissolve away in only a few minutes.
Re: Grenadier's big thread of Röntgen related shenanigans
Proud Mary, Thu Nov 25 2010, 08:01PM
That sounds exciting! I'll be interested to hear how you get on with that.
Proud Mary, Thu Nov 25 2010, 08:01PM
Klugesmith wrote ...
By coincidence, speaking of shielding boxes, I'm about to find out if 5/8" drywall (gypsum board) can practically block x-rays at NST voltage (15 kV RMS). If so, then I'll make a box out of that, this weekend, and play at the limited voltage before getting out the lead and the oil.
By coincidence, speaking of shielding boxes, I'm about to find out if 5/8" drywall (gypsum board) can practically block x-rays at NST voltage (15 kV RMS). If so, then I'll make a box out of that, this weekend, and play at the limited voltage before getting out the lead and the oil.
That sounds exciting! I'll be interested to hear how you get on with that.
Re: Grenadier's big thread of Röntgen related shenanigans
klugesmith, Thu Nov 25 2010, 08:08PM
At one summer job we used sacks of shot as weights to hold things down.
One had been creatively modified, sort of like this picture was modified today.
Except in the 70's, the word LEAD was implicit & did not appear on the sack label.
klugesmith, Thu Nov 25 2010, 08:08PM
Grenadier wrote ...
Y'know what you can do for short experiments is mix lead shot with plaster of paris. That would make castable, yet brittle and clunky shielding. It'd be good for short experiments though. The best part about it is that you can get your lead shit back by simply dissolving the plaster in HCl.
Did you change the vowel in shot on purpose? Y'know what you can do for short experiments is mix lead shot with plaster of paris. That would make castable, yet brittle and clunky shielding. It'd be good for short experiments though. The best part about it is that you can get your lead shit back by simply dissolving the plaster in HCl.
At one summer job we used sacks of shot as weights to hold things down.
One had been creatively modified, sort of like this picture was modified today.
Except in the 70's, the word LEAD was implicit & did not appear on the sack label.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Fri Nov 26 2010, 12:18AM
Lol oops. If I ever come across bags of lead shot I'll be sure to have a sharpie on hand.
Adam Munich, Fri Nov 26 2010, 12:18AM
Lol oops. If I ever come across bags of lead shot I'll be sure to have a sharpie on hand.
Re: Grenadier's big thread of Röntgen related shenanigans
klugesmith, Fri Nov 26 2010, 01:42AM
Not to steal Grenadier's thread, but here are the early results.
Experiment: connect a little Coolidge tube across 15 kV NST (with momentary-contact switch). Heat filament enough for 1 mA average anode current. Aim at Geiger counter about 8 inches away, and interpose experimental materials attempting to block the x-rays. (The counter responds vigorously with half the voltage and 1 microamp of anode current).
No way in hell:
1/2 inch drywall
1 inch drywall -- this was disappointing, it ain't 1 inch of crystalline CaSO4.2H2O for sure
1/4 inch cement-based backer board
0.1 inch glass
0.063 aluminum
0.019 steel
marginal:
1/4 inch FR-4 fiberglass
0.027 steel
probably good:
0.050 steel (a sheet-metal bookend)
0.125 steel
3/4 inch thick terra-cotta quarry tile
klugesmith, Fri Nov 26 2010, 01:42AM
Proud Mary wrote ...
Klugesmith wrote ...
By coincidence, speaking of shielding boxes, I'm about to find out if 5/8" drywall (gypsum board) can practically block x-rays at NST voltage (15 kV RMS). If so, then I'll make a box out of that, this weekend, and play at the limited voltage before getting out the lead and the oil.
That sounds exciting! I'll be interested to hear how you get on with that. By coincidence, speaking of shielding boxes, I'm about to find out if 5/8" drywall (gypsum board) can practically block x-rays at NST voltage (15 kV RMS). If so, then I'll make a box out of that, this weekend, and play at the limited voltage before getting out the lead and the oil.
Not to steal Grenadier's thread, but here are the early results.
Experiment: connect a little Coolidge tube across 15 kV NST (with momentary-contact switch). Heat filament enough for 1 mA average anode current. Aim at Geiger counter about 8 inches away, and interpose experimental materials attempting to block the x-rays. (The counter responds vigorously with half the voltage and 1 microamp of anode current).
No way in hell:
1/2 inch drywall
1 inch drywall -- this was disappointing, it ain't 1 inch of crystalline CaSO4.2H2O for sure
1/4 inch cement-based backer board
0.1 inch glass
0.063 aluminum
0.019 steel
marginal:
1/4 inch FR-4 fiberglass
0.027 steel
probably good:
0.050 steel (a sheet-metal bookend)
0.125 steel
3/4 inch thick terra-cotta quarry tile
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Fri Nov 26 2010, 02:02AM
No problem, I encourage thread hijacking. It leads to conversations and discoveries that might've never happened otherwise. Sorry to hear about your gypsum failure. I had a feeling that it wasn't going to stop anything. Also remember a 15kV NST has a peak voltage 21kV.
Adam Munich, Fri Nov 26 2010, 02:02AM
No problem, I encourage thread hijacking. It leads to conversations and discoveries that might've never happened otherwise. Sorry to hear about your gypsum failure. I had a feeling that it wasn't going to stop anything. Also remember a 15kV NST has a peak voltage 21kV.
Re: Grenadier's big thread of Röntgen related shenanigans
Proud Mary, Fri Nov 26 2010, 09:05AM
In the gypsum board/CaSo4 experiment, Ca characteristic rays will have been added to those photons which transit the gypsum board unmodified, so whilst there can only be a net loss, it will not have been as great as might have been expected from other material of similar density
The iron in your steel will also have emitted its characteristic rays, but what photons of its 6keV peak made it through to the other side of the steel, and through the air, will not have made it through the counting tube wall.
For the benefit of the uninitiated casual reader of this thread, I feel I should point out that even a teensy weensy little X-ray tube like the famous Svetlana BS7 with its maximum anode voltage of 15kV @ 50uA will still produce a dose rate of ~1000Sv/hr at 1 cm from the beryllium exit window - so just a few minutes of casual handling of the live tube is likely to lead to ulceration and necrosis of the skin, and other irreversible changes.
Proud Mary, Fri Nov 26 2010, 09:05AM
Klugesmith wrote ...
Not to steal Grenadier's thread, but here are the early results.
Experiment: connect a little Coolidge tube across 15 kV NST (with momentary-contact switch). Heat filament enough for 1 mA average anode current. Aim at Geiger counter about 8 inches away, and interpose experimental materials attempting to block the x-rays. (The counter responds vigorously with half the voltage and 1 microamp of anode current).
No way in hell:
1/2 inch drywall
1 inch drywall -- this was disappointing, it ain't 1 inch of crystalline CaSO4.2H2O for sure
1/4 inch cement-based backer board
0.1 inch glass
0.063 aluminum
0.019 steel
marginal:
1/4 inch FR-4 fiberglass
0.027 steel
probably good:
0.050 steel (a sheet-metal bookend)
0.125 steel
3/4 inch thick terra-cotta quarry tile
Proud Mary wrote ...
Klugesmith wrote ...
By coincidence, speaking of shielding boxes, I'm about to find out if 5/8" drywall (gypsum board) can practically block x-rays at NST voltage (15 kV RMS). If so, then I'll make a box out of that, this weekend, and play at the limited voltage before getting out the lead and the oil.
That sounds exciting! I'll be interested to hear how you get on with that. By coincidence, speaking of shielding boxes, I'm about to find out if 5/8" drywall (gypsum board) can practically block x-rays at NST voltage (15 kV RMS). If so, then I'll make a box out of that, this weekend, and play at the limited voltage before getting out the lead and the oil.
Not to steal Grenadier's thread, but here are the early results.
Experiment: connect a little Coolidge tube across 15 kV NST (with momentary-contact switch). Heat filament enough for 1 mA average anode current. Aim at Geiger counter about 8 inches away, and interpose experimental materials attempting to block the x-rays. (The counter responds vigorously with half the voltage and 1 microamp of anode current).
No way in hell:
1/2 inch drywall
1 inch drywall -- this was disappointing, it ain't 1 inch of crystalline CaSO4.2H2O for sure
1/4 inch cement-based backer board
0.1 inch glass
0.063 aluminum
0.019 steel
marginal:
1/4 inch FR-4 fiberglass
0.027 steel
probably good:
0.050 steel (a sheet-metal bookend)
0.125 steel
3/4 inch thick terra-cotta quarry tile
In the gypsum board/CaSo4 experiment, Ca characteristic rays will have been added to those photons which transit the gypsum board unmodified, so whilst there can only be a net loss, it will not have been as great as might have been expected from other material of similar density
The iron in your steel will also have emitted its characteristic rays, but what photons of its 6keV peak made it through to the other side of the steel, and through the air, will not have made it through the counting tube wall.
For the benefit of the uninitiated casual reader of this thread, I feel I should point out that even a teensy weensy little X-ray tube like the famous Svetlana BS7 with its maximum anode voltage of 15kV @ 50uA will still produce a dose rate of ~1000Sv/hr at 1 cm from the beryllium exit window - so just a few minutes of casual handling of the live tube is likely to lead to ulceration and necrosis of the skin, and other irreversible changes.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Sat Nov 27 2010, 09:44PM
Well soldering went off without a hitch. At first it wouldn't work with the pen torch, but it was smooth sailing once the 40 watt iron joined the party.
Supplies.
I sure hope that's a right angle.
I decided to burn from the outside.
Tack soldering did help alot.
It looks right.
Well, pretty close to right, but needs a little help.
5 sides now.
Time to start seam burning.
Things really got sturdy when I burned the seams.
Complete!
The lid fits nicely.
Is it water tight?
Overall it took me only three hours to put it together, and it was a lot easier than expected. One thing if certain: this box isn't going to come apart again in only 6 pieces. I'm a pretty good leadsmith if I do say so myself.
Adam Munich, Sat Nov 27 2010, 09:44PM
Well soldering went off without a hitch. At first it wouldn't work with the pen torch, but it was smooth sailing once the 40 watt iron joined the party.
Supplies.
I sure hope that's a right angle.
I decided to burn from the outside.
Tack soldering did help alot.
It looks right.
Well, pretty close to right, but needs a little help.
5 sides now.
Time to start seam burning.
Things really got sturdy when I burned the seams.
Complete!
The lid fits nicely.
Is it water tight?
Overall it took me only three hours to put it together, and it was a lot easier than expected. One thing if certain: this box isn't going to come apart again in only 6 pieces. I'm a pretty good leadsmith if I do say so myself.
Re: Grenadier's big thread of Röntgen related shenanigans
klugesmith, Sun Nov 28 2010, 06:48AM
How come your cat isn't in any of the pictures this time?
klugesmith, Sun Nov 28 2010, 06:48AM
How come your cat isn't in any of the pictures this time?
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Sun Nov 28 2010, 07:02AM
She doesn't like fire.
Adam Munich, Sun Nov 28 2010, 07:02AM
She doesn't like fire.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Tue Nov 30 2010, 08:03AM
Lately I've been trying to figure out how to make a 12V battery powered variable HVDC supply for this thing. I figured why bother making it modular when I can just build this aforementioned supply and use a step-down xformer to run it off the mains.
So, any ideas? Ideally it would supply 20 to 70kV, and at least 3mA.
Adam Munich, Tue Nov 30 2010, 08:03AM
Lately I've been trying to figure out how to make a 12V battery powered variable HVDC supply for this thing. I figured why bother making it modular when I can just build this aforementioned supply and use a step-down xformer to run it off the mains.
So, any ideas? Ideally it would supply 20 to 70kV, and at least 3mA.
Re: Grenadier's big thread of Röntgen related shenanigans
uzzors2k, Tue Nov 30 2010, 06:18PM
Mazzilli ZVS driver + AC flyback + C&W multiplier is your best bet.
uzzors2k, Tue Nov 30 2010, 06:18PM
Mazzilli ZVS driver + AC flyback + C&W multiplier is your best bet.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Wed Dec 01 2010, 12:18AM
I was thinking of something with an induction coil. Not only would a CW require pretty expensive capacitors, Finding a suitable AC flyback would be a job in itself.
Remember, I need to make the voltage adjustable too. I'm not too sure how to accomplish that. A tapped CW might work, but to have any real good control I'll need a whole crap load of stages, and a whole crap load of switches to control where the tap is.
Adam Munich, Wed Dec 01 2010, 12:18AM
I was thinking of something with an induction coil. Not only would a CW require pretty expensive capacitors, Finding a suitable AC flyback would be a job in itself.
Remember, I need to make the voltage adjustable too. I'm not too sure how to accomplish that. A tapped CW might work, but to have any real good control I'll need a whole crap load of stages, and a whole crap load of switches to control where the tap is.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Sat Dec 04 2010, 03:53AM
OK change of plans. I'm not going to use that giant lead box, so all that work was for not. It's still a really cool thing though, so I'm certainly not going to get rid of it, maybe I can store the uranium (that I'm still hoping to buy) in it.
What made me change my mind? Well I bought an x-ray tube, and it came today. Look at it:
Tube
Lol
Heh, that certainly wasn't what I as expecting. If I wanted to I could make this thing handheld!
So now I'm back to square one. I don't think I'm going to cast a new box, because I have enough lead sheet to make a box for this thing 1cm thick. I'm kind of happy that I'm not using this big box. Why? It's heavy. Now that I'm not using it I can make this machine much more compact, and I have a lot of "weight space" to build the PSU, the battery, and the arduino controlling circuity.
Thanks goes to X-ray for providing this awesome tube. .8mm focal spot, 7ma @ 70kV. This is going to be one hell of an xray machine.
Just in case anyone was wondering, I copied and pasted all the r's w's and the q.
Adam Munich, Sat Dec 04 2010, 03:53AM
OK change of plans. I'm not going to use that giant lead box, so all that work was for not. It's still a really cool thing though, so I'm certainly not going to get rid of it, maybe I can store the uranium (that I'm still hoping to buy) in it.
What made me change my mind? Well I bought an x-ray tube, and it came today. Look at it:
Tube
Lol
Heh, that certainly wasn't what I as expecting.
If I wanted to I could make this thing handheld!So now I'm back to square one. I don't think I'm going to cast a new box, because I have enough lead sheet to make a box for this thing 1cm thick. I'm kind of happy that I'm not using this big box. Why? It's heavy. Now that I'm not using it I can make this machine much more compact, and I have a lot of "weight space" to build the PSU, the battery, and the arduino controlling circuity.
Thanks goes to X-ray for providing this awesome tube. .8mm focal spot, 7ma @ 70kV. This is going to be one hell of an xray machine.
Just in case anyone was wondering, I copied and pasted all the r's w's and the q.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Wed Mar 09 2011, 04:21AM
Alright, no more procrastinating. This is what I've got so far....
The lead shield is 3mm thick, I need to make it 7mm thick. That should be plenty to block the 75kV rays. I also need to drill some holes in it and make a lid.
The tube is being held in a tupperware inside the shield. It'll be filled with olive oil and if I did my maths right it can store about 22kJ of heat before it gets 30 or so degrees hotter.
The CW is in a tupperware too and will be filled with oil, and it'll be powered via a ZVS at about 60khz. I need to make HV feedthroughs in both tupperwares, I think something involving plastic tubes and JB weld might work. The wire connecting the two containers needs to have very thick insulation, I'm thinking some projection TV wire and a bunch of electrical tape could work.
I need to get a 22V lipo, hopefully my other CW sells soon so I can buy it. Power will be adjustable from 17 to 21V via an LM317 + 2n3055 and I'm going to need to find a hefty TO3 heatsink as this thing will be dissipating lots of watts, though it won't be run continuously. The power will be applied to the circuit via a mechanical relay as there is a very little chance it'll fail closed circuit. Exposure time will be controlled by an arduino, which will also monitor the temperature of the 2n3055, the tube oil, and the battery voltage. Possibly I can make this thing radio controlled too, rather than a long wire as a trigger.
Heater voltage will be fixed at 2.6V, and that will allow 3mA through the tube if the graphs are right. Not sure how to go about this, maybe d batteries and a rheostat. I'm kind of afraid that an LM317 will die due to electrostatics from the CW.
I think the box is a little too small. Hopefully AC moore will let me return it w/o a receipt (lost it).
Adam Munich, Wed Mar 09 2011, 04:21AM
Alright, no more procrastinating. This is what I've got so far....
The lead shield is 3mm thick, I need to make it 7mm thick. That should be plenty to block the 75kV rays. I also need to drill some holes in it and make a lid.
The tube is being held in a tupperware inside the shield. It'll be filled with olive oil and if I did my maths right it can store about 22kJ of heat before it gets 30 or so degrees hotter.
The CW is in a tupperware too and will be filled with oil, and it'll be powered via a ZVS at about 60khz. I need to make HV feedthroughs in both tupperwares, I think something involving plastic tubes and JB weld might work. The wire connecting the two containers needs to have very thick insulation, I'm thinking some projection TV wire and a bunch of electrical tape could work.
I need to get a 22V lipo, hopefully my other CW sells soon so I can buy it. Power will be adjustable from 17 to 21V via an LM317 + 2n3055 and I'm going to need to find a hefty TO3 heatsink as this thing will be dissipating lots of watts, though it won't be run continuously. The power will be applied to the circuit via a mechanical relay as there is a very little chance it'll fail closed circuit. Exposure time will be controlled by an arduino, which will also monitor the temperature of the 2n3055, the tube oil, and the battery voltage. Possibly I can make this thing radio controlled too, rather than a long wire as a trigger.
Heater voltage will be fixed at 2.6V, and that will allow 3mA through the tube if the graphs are right. Not sure how to go about this, maybe d batteries and a rheostat. I'm kind of afraid that an LM317 will die due to electrostatics from the CW.
I think the box is a little too small. Hopefully AC moore will let me return it w/o a receipt (lost it).
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Fri Mar 11 2011, 04:22AM
Yay, AC moore let me exchange box. I got 2 smaller ones, plan on gluing them together. All the electronics will be in one box while the HV stuff will be in the other. That should be enough HV isolation...
I started to make the primary coil feedthroughs on the CW case, I used brass hardware because it's solderable. Testing indicates that it is oilproof, so yay!
Tube heater is going to be fixed at 2.8V to limit current at about 3mA \, and the heater will be powered by D cells. Maybe I'll have a voltmeter on the back that tells me the heater voltage, too low/hi I'll open up the box and adjust the stat.
I've been thinking about anode current monitoring and I realized that it can be measured simply by putting a 5mA meter in series with HV ground. So I need a 5V meter and a 5mA meter. Hmm.... where get?
As for the lead shield, so far it is 5mm. I was aiming for 7mm, but I found this transmission calculator and according to it:
5mm Pb has a transmittance of 6.59e-22 at 50kVp
5mm Pb has a transmittance of 1.26e-13 at 70kVp
5mm Pb has a transmittance of 1.72e-8 at 90kVp
So assuming 30Sv/min of radiation that means
@50kVp that's immeasurable
@70kVp that's 0.00378 nSv/min
@90kVp that's .516 uSv/min
I'll be 10 feet away from this thing while it's on (obviously not in the beam path) so if these numbers are correct then compton scattering is a bigger problem than direct exposure from the tube!
Proud Mary, you are the radiation expert, so does this seem correct to you?
Adam Munich, Fri Mar 11 2011, 04:22AM
Yay, AC moore let me exchange box. I got 2 smaller ones, plan on gluing them together. All the electronics will be in one box while the HV stuff will be in the other. That should be enough HV isolation...
I started to make the primary coil feedthroughs on the CW case, I used brass hardware because it's solderable. Testing indicates that it is oilproof, so yay!
Tube heater is going to be fixed at 2.8V to limit current at about 3mA \, and the heater will be powered by D cells. Maybe I'll have a voltmeter on the back that tells me the heater voltage, too low/hi I'll open up the box and adjust the stat.
I've been thinking about anode current monitoring and I realized that it can be measured simply by putting a 5mA meter in series with HV ground. So I need a 5V meter and a 5mA meter. Hmm.... where get?
As for the lead shield, so far it is 5mm. I was aiming for 7mm, but I found this transmission calculator
and according to it:5mm Pb has a transmittance of 6.59e-22 at 50kVp
5mm Pb has a transmittance of 1.26e-13 at 70kVp
5mm Pb has a transmittance of 1.72e-8 at 90kVp
So assuming 30Sv/min of radiation that means
@50kVp that's immeasurable
@70kVp that's 0.00378 nSv/min
@90kVp that's .516 uSv/min
I'll be 10 feet away from this thing while it's on (obviously not in the beam path) so if these numbers are correct then compton scattering is a bigger problem than direct exposure from the tube!
Proud Mary, you are the radiation expert, so does this seem correct to you?
Re: Grenadier's big thread of Röntgen related shenanigans
Proud Mary, Fri Mar 11 2011, 11:55AM
Well now, if we say your worst case is Va 90kV, Ia 7mA, with 5mm Pb shielding, the dose-rate centre-beam at 3000 mm will be of the order of 100 μSv/hr.
What sort of dose-rate is 100 μSv/hr? In radiogeology, it's a rule of thumb reckoning on the dose-rate you'd expect to get when standing on top of a planar pitchblende load, or the gamma reading you get when you put a GM tube right up to a chunk of best quality pitchblende.
It means that if you did a 10 second radiography exposure you'd receive 0.03 μSv, not a lot, it's true, but still a figure to be added to your cumulative life time dose.
Without the 5mm Pb shield, the dose rate rises to about 2 Sv/hr:
The Bells of Hell go ting-a-ling-a-ling
For you but not for me:
For me the angels sing-a-ling-a-ling,
They've got the goods for me.
If we go for a more prudent 50kV/1mA, with your 5mm Pb shielding, then the dose-rate at 3000 mm will be about 3E-6 μSv/hr - below the theshold of detection for all normal radiological protection purposes.
There are far too many variables and unknowns for any sort of accuracy in these generalised calculations, so you should consider these figures as a very rough guide only, figures to be confirmed by real world dosimetry.
Proud Mary, Fri Mar 11 2011, 11:55AM
Grenadier wrote ...
Yay, AC moore let me exchange box. I got 2 smaller ones, plan on gluing them together. All the electronics will be in one box while the HV stuff will be in the other. That should be enough HV isolation...
I started to make the primary coil feedthroughs on the CW case, I used brass hardware because it's solderable. Testing indicates that it is oilproof, so yay!
Tube heater is going to be fixed at 2.8V to limit current at about 3mA \, and the heater will be powered by D cells. Maybe I'll have a voltmeter on the back that tells me the heater voltage, too low/hi I'll open up the box and adjust the stat.
I've been thinking about anode current monitoring and I realized that it can be measured simply by putting a 5mA meter in series with HV ground. So I need a 5V meter and a 5mA meter. Hmm.... where get?
As for the lead shield, so far it is 5mm. I was aiming for 7mm, but I found this transmission calculator and according to it:
5mm Pb has a transmittance of 6.59e-22 at 50kVp
5mm Pb has a transmittance of 1.26e-13 at 70kVp
5mm Pb has a transmittance of 1.72e-8 at 90kVp
So assuming 30Sv/min of radiation that means
@50kVp that's immeasurable
@70kVp that's 0.00378 nSv/min
@90kVp that's .516 uSv/min
I'll be 10 feet away from this thing while it's on (obviously not in the beam path) so if these numbers are correct then compton scattering is a bigger problem than direct exposure from the tube!
Proud Mary, you are the radiation expert, so does this seem correct to you?
Yay, AC moore let me exchange box. I got 2 smaller ones, plan on gluing them together. All the electronics will be in one box while the HV stuff will be in the other. That should be enough HV isolation...
I started to make the primary coil feedthroughs on the CW case, I used brass hardware because it's solderable. Testing indicates that it is oilproof, so yay!
Tube heater is going to be fixed at 2.8V to limit current at about 3mA \, and the heater will be powered by D cells. Maybe I'll have a voltmeter on the back that tells me the heater voltage, too low/hi I'll open up the box and adjust the stat.
I've been thinking about anode current monitoring and I realized that it can be measured simply by putting a 5mA meter in series with HV ground. So I need a 5V meter and a 5mA meter. Hmm.... where get?
As for the lead shield, so far it is 5mm. I was aiming for 7mm, but I found this transmission calculator
and according to it:5mm Pb has a transmittance of 6.59e-22 at 50kVp
5mm Pb has a transmittance of 1.26e-13 at 70kVp
5mm Pb has a transmittance of 1.72e-8 at 90kVp
So assuming 30Sv/min of radiation that means
@50kVp that's immeasurable
@70kVp that's 0.00378 nSv/min
@90kVp that's .516 uSv/min
I'll be 10 feet away from this thing while it's on (obviously not in the beam path) so if these numbers are correct then compton scattering is a bigger problem than direct exposure from the tube!
Proud Mary, you are the radiation expert, so does this seem correct to you?
Well now, if we say your worst case is Va 90kV, Ia 7mA, with 5mm Pb shielding, the dose-rate centre-beam at 3000 mm will be of the order of 100 μSv/hr.
What sort of dose-rate is 100 μSv/hr? In radiogeology, it's a rule of thumb reckoning on the dose-rate you'd expect to get when standing on top of a planar pitchblende load, or the gamma reading you get when you put a GM tube right up to a chunk of best quality pitchblende.
It means that if you did a 10 second radiography exposure you'd receive 0.03 μSv, not a lot, it's true, but still a figure to be added to your cumulative life time dose.
Without the 5mm Pb shield, the dose rate rises to about 2 Sv/hr:
The Bells of Hell go ting-a-ling-a-ling
For you but not for me:
For me the angels sing-a-ling-a-ling,
They've got the goods for me.
If we go for a more prudent 50kV/1mA, with your 5mm Pb shielding, then the dose-rate at 3000 mm will be about 3E-6 μSv/hr - below the theshold of detection for all normal radiological protection purposes.
There are far too many variables and unknowns for any sort of accuracy in these generalised calculations, so you should consider these figures as a very rough guide only, figures to be confirmed by real world dosimetry.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Fri Mar 11 2011, 08:32PM
Hmm... Well I'm not going to be center beam for obvious reasons, instead I'll be behind the machine and thus behind the angled tungsten anode. Therefore there should be little radiation there to begin with as the tungsten will block most of it. I suppose I could add one more mm of Pb, or better yet I could make a small Pb jacket for the tube, which would be light and easy to make. I could also step back another 8 or so feet.
I never intend to run the thing at 90kVp, that's just the worst case scenario where the regulator fails and the full 22.7V from the lipo goes into the CW. (pretty sure it'll give 90kV in that case). Also, the tube will probably 'splode if it runs for more than 5 or so minutes, so a failure would be self limiting. The MCU will measure the temp anyway and kill the CW's power if there is an issue. I plan on using 2 relays in series, so if one fails the thing can still be turned off. The more protection the better, and components are cheaper than hospital bills.
May I ask what formulas you used to calculate that PM?
Adam Munich, Fri Mar 11 2011, 08:32PM
Hmm... Well I'm not going to be center beam for obvious reasons, instead I'll be behind the machine and thus behind the angled tungsten anode. Therefore there should be little radiation there to begin with as the tungsten will block most of it. I suppose I could add one more mm of Pb, or better yet I could make a small Pb jacket for the tube, which would be light and easy to make. I could also step back another 8 or so feet.
I never intend to run the thing at 90kVp, that's just the worst case scenario where the regulator fails and the full 22.7V from the lipo goes into the CW. (pretty sure it'll give 90kV in that case). Also, the tube will probably 'splode if it runs for more than 5 or so minutes, so a failure would be self limiting. The MCU will measure the temp anyway and kill the CW's power if there is an issue. I plan on using 2 relays in series, so if one fails the thing can still be turned off. The more protection the better, and components are cheaper than hospital bills.
May I ask what formulas you used to calculate that PM?
Re: Grenadier's big thread of Röntgen related shenanigans
Proud Mary, Fri Mar 11 2011, 10:22PM
This should set you straight for the moment:
You can see at a glance why I never do more than 50kV.
If you want to get a bit deeper into the theory of shielding, you can't go far wrong with NIST: X-Ray Mass Attenuation Coefficients here:
Proud Mary, Fri Mar 11 2011, 10:22PM
This should set you straight for the moment:
You can see at a glance why I never do more than 50kV.
If you want to get a bit deeper into the theory of shielding, you can't go far wrong with NIST: X-Ray Mass Attenuation Coefficients here:
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Sat Mar 19 2011, 04:44AM
Alright, work has been a little slow but this is what I've got so far.
I scratched my head for hours and cursed at a bunch of adhesive bottles because I couldn't get anything to stick to the polypropylene Tupperware. About to give up I grabbed my hot glue gun and tried that for the hell of it and what do ya know, it glued the PP, and did a fine job of it too. Let the records show that hot glue is the only thing that bonds PP.
This is the HV feedthough I came up with. It consists of a rubber insulated wire inside an aquarium tube inside some random tube I found behind the sofa. A bic pen was also used. Here's a paint image that details what I did.
It seems to be putting out more than 1mA of current, and judging by how fast the meter was pegged I'd say it's about 1.7mA. I need a bigger meter.
I'm not sure if I want to leave the current limiting resistor in or take it out when I connect the tube up. I don't want to accidentally kill my 20mA diodes... nonetheless I need to order some parts, mainly the 5mA meter, the 5V meter and the 22v lipo. I plan on ordering that stuff tomorrow. I'm not sure yet if I want to monitor the anode voltage with a resistive voltage divider and yet another meter.
I don't want to use analog meters for the x-ray because well I won't be able to read them from 15 feet away. But digital ones might not like being connected to the CW. Even though their voltages are not going to be exceeded they might build up a static charge and bust...
Hmm decisions decisions...
Adam Munich, Sat Mar 19 2011, 04:44AM
Alright, work has been a little slow but this is what I've got so far.
I scratched my head for hours and cursed at a bunch of adhesive bottles because I couldn't get anything to stick to the polypropylene Tupperware. About to give up I grabbed my hot glue gun and tried that for the hell of it and what do ya know, it glued the PP, and did a fine job of it too. Let the records show that hot glue is the only thing that bonds PP.
This is the HV feedthough I came up with. It consists of a rubber insulated wire inside an aquarium tube inside some random tube I found behind the sofa. A bic pen was also used. Here's a paint image that details what I did. 
It seems to be putting out more than 1mA of current, and judging by how fast the meter was pegged I'd say it's about 1.7mA. I need a bigger meter.
I'm not sure if I want to leave the current limiting resistor in or take it out when I connect the tube up. I don't want to accidentally kill my 20mA diodes... nonetheless I need to order some parts, mainly the 5mA meter, the 5V meter and the 22v lipo. I plan on ordering that stuff tomorrow. I'm not sure yet if I want to monitor the anode voltage with a resistive voltage divider and yet another meter.
I don't want to use analog meters for the x-ray because well I won't be able to read them from 15 feet away. But digital ones might not like being connected to the CW. Even though their voltages are not going to be exceeded they might build up a static charge and bust...
Hmm decisions decisions...
Re: Grenadier's big thread of Röntgen related shenanigans
radhoo, Sat Mar 19 2011, 10:46AM
An exciting thread, looking forward to your first results!
Soon, probably in a month or two, oil will leak around the HV connector. Hot glue is dissolved, but even worse, you seem to have a few little pipes that will encourage the capillarity effect. Best thing would have been to use a simple metallic screw, uninsulated but strongly pressing the plastic wall. Then over it you could have applied epoxy or hot glue as an insulator. This would hold better, but... the plastic contains air, so in time between the pressing screw and the plastic wall a gap would develop. So the final solution would be a tight screw and a rubber fitting. Just my 2 cents.
Regarding the decisions on the measuring instrument: using digital will fail. On my low voltage variable supply (30V max) I use a cheap chinese voltmeter based on some unknown uC . A few spikes and its dead, despite the protection with neon lamp, zener diode or other filters. You should really get an analog meter.
For the readings you can always set the camera on the tripod and make a short film. Then turn the lights off and do whatever you want to experiment.
radhoo, Sat Mar 19 2011, 10:46AM
An exciting thread, looking forward to your first results!
Soon, probably in a month or two, oil will leak around the HV connector. Hot glue is dissolved, but even worse, you seem to have a few little pipes that will encourage the capillarity effect. Best thing would have been to use a simple metallic screw, uninsulated but strongly pressing the plastic wall. Then over it you could have applied epoxy or hot glue as an insulator. This would hold better, but... the plastic contains air, so in time between the pressing screw and the plastic wall a gap would develop. So the final solution would be a tight screw and a rubber fitting. Just my 2 cents.
Regarding the decisions on the measuring instrument: using digital will fail. On my low voltage variable supply (30V max) I use a cheap chinese voltmeter based on some unknown uC . A few spikes and its dead, despite the protection with neon lamp, zener diode or other filters. You should really get an analog meter.
For the readings you can always set the camera on the tripod and make a short film. Then turn the lights off and do whatever you want to experiment.
Re: Grenadier's big thread of Röntgen related shenanigans
Proud Mary, Sat Mar 19 2011, 12:04PM
I agree with Radu 100% here, and use moving coil panel meters for measuring X-ray cathode and filament/heater current. I connect one side of the meter to Earth, and put a gas discharge arrestor across it to stop the meter becoming 'live' if it fails open circuit.
Proud Mary, Sat Mar 19 2011, 12:04PM
radhoo wrote ...
Regarding the decisions on the measuring instrument: using digital will fail. On my low voltage variable supply (30V max) I use a cheap chinese voltmeter based on some unknown uC . A few spikes and its dead, despite the protection with neon lamp, zener diode or other filters. You should really get an analog meter.
For the readings you can always set the camera on the tripod and make a short film. Then turn the lights off and do whatever you want to experiment.
Regarding the decisions on the measuring instrument: using digital will fail. On my low voltage variable supply (30V max) I use a cheap chinese voltmeter based on some unknown uC . A few spikes and its dead, despite the protection with neon lamp, zener diode or other filters. You should really get an analog meter.
For the readings you can always set the camera on the tripod and make a short film. Then turn the lights off and do whatever you want to experiment.
I agree with Radu 100% here, and use moving coil panel meters for measuring X-ray cathode and filament/heater current. I connect one side of the meter to Earth, and put a gas discharge arrestor across it to stop the meter becoming 'live' if it fails open circuit.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Sat Mar 19 2011, 12:10PM
Yes, it's already leaking. It's leaking slowly, but it is leaking...
Grr... the hole is nearly 1/4" now, way too big for a screw and I don't have a similar piece of tupperware. What do?
Edit: I'm going to go get some o-rings and small fender washers, maybe I can seal the hole with that and a screw.
Adam Munich, Sat Mar 19 2011, 12:10PM
Yes, it's already leaking. It's leaking slowly, but it is leaking...
Grr... the hole is nearly 1/4" now, way too big for a screw and I don't have a similar piece of tupperware. What do?
Edit: I'm going to go get some o-rings and small fender washers, maybe I can seal the hole with that and a screw.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Sat Mar 19 2011, 09:49PM
Alright, I fixed the HV feedthrough problem, yet the CW *still* leaks. This time it's oil seeping out of the lid, and I can't get it sealed...
I'm thinking about taking all the caps and diodes off the PCB and point to point wiring the CW so it's nice and "skinny". Then I can put it in a PVC tube or something, because this container just does not want to keep oil inside, and I can't glue it because its polyethylene.
Adam Munich, Sat Mar 19 2011, 09:49PM
Alright, I fixed the HV feedthrough problem, yet the CW *still* leaks. This time it's oil seeping out of the lid, and I can't get it sealed...
I'm thinking about taking all the caps and diodes off the PCB and point to point wiring the CW so it's nice and "skinny". Then I can put it in a PVC tube or something, because this container just does not want to keep oil inside, and I can't glue it because its polyethylene.
Re: Grenadier's big thread of Röntgen related shenanigans
Conundrum, Sat Mar 19 2011, 11:14PM
superglue and baking soda on the outside, sand down the edges and coat with superglue accelerant to provide a keying point?
Just a thought.
-A
Conundrum, Sat Mar 19 2011, 11:14PM
superglue and baking soda on the outside, sand down the edges and coat with superglue accelerant to provide a keying point?
Just a thought.
-A
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Mon Mar 21 2011, 02:24AM
I gave up with the tupperware. Instead I opted for PVC pipe.
To fit the cw in there I needed to shrink it (no pcb).
After that I got some PVC pipe and fittings to make the case, then I made some feedthroughs with brass bolts and sealing washers, then I slid the CW in there and superglued it in place.
I am leaving the current limiting resistor in, mainly because if I left it out I'd probably do something stupid and blow all the diodes. Those carbon comp resistors are indestructible.
Here is the completed CW. The threaded fitting is held on with pvc cement, while the end cap is just going to be slid on and hot glued (to allow for modification).
The flyback needed its own container, so i found some tupperware that doesn't leak.
And then I proceeded to put the FBT in there. I ran out of hardware though and so it sits on my floor until tomorrow.
Here is the tube shield I made today.
And here is everything so far. There is still some room for the heater batteries and rheostat, so yay.
Also, it is going to take more than 22V to make 75kV, so I'm going to need both a 6s lipo and a 1 or 2s lipo to put in series.
Adam Munich, Mon Mar 21 2011, 02:24AM
I gave up with the tupperware. Instead I opted for PVC pipe.
To fit the cw in there I needed to shrink it (no pcb).
After that I got some PVC pipe and fittings to make the case, then I made some feedthroughs with brass bolts and sealing washers, then I slid the CW in there and superglued it in place.
I am leaving the current limiting resistor in, mainly because if I left it out I'd probably do something stupid and blow all the diodes. Those carbon comp resistors are indestructible.
Here is the completed CW. The threaded fitting is held on with pvc cement, while the end cap is just going to be slid on and hot glued (to allow for modification).
The flyback needed its own container, so i found some tupperware that doesn't leak.
And then I proceeded to put the FBT in there. I ran out of hardware though and so it sits on my floor until tomorrow.
Here is the tube shield I made today.
And here is everything so far. There is still some room for the heater batteries and rheostat, so yay.
Also, it is going to take more than 22V to make 75kV, so I'm going to need both a 6s lipo and a 1 or 2s lipo to put in series.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Tue Mar 22 2011, 02:03AM
Today's progress.
The Hot glue seal leaked on the CW, so I removed that and just dripped PVC cement on the seam. That will both seal it and allow for removal if need be. I then covered the CW with electrical tape because I was bored.
After that I finished the flyback's container. The FBT is held in place by its primary winding, and it seems to be staying put.
I then connected everything up for a test. The entire circuit puts out 75 to 80kV at 31V in. I'm not sure why, when it used to do the same at only 22V in some weeks ago. I presume that this is because there are corona losses from the external wiring, but I'm not going to bother fighting it. 31V is just a 6s and a 3s lipo in series.
I'm probably going to buy a 3000mAh lipos, they should provide me with 30 1 minute exposures which is more than plenty. I'm not buying the lipos until I get the linear regulator done, and that is on this week's to-do list.
Some sparking next to an m&m at full power. It hurts my ears. EDIT 4got the video
As for the tube, I got the feedthroughs made, now I need to figure out how to insulate the HV feedthrough from the lead container. I'm thinking a PVC tube and loads of hot glue.
As for the tube I've been playing with the heater, and it definitely doesn't need many volts to get hot. Here is a "hotness chart" I have prepared just by looking at the light. I'm going to limit it at 2V which should give me 2.5 or so mA of anode current.
Some heater pics
@1.5V
@2V
And after all of these modifications there is no more leaking :D
Adam Munich, Tue Mar 22 2011, 02:03AM
Today's progress.
The Hot glue seal leaked on the CW, so I removed that and just dripped PVC cement on the seam. That will both seal it and allow for removal if need be.
I then covered the CW with electrical tape because I was bored.After that I finished the flyback's container. The FBT is held in place by its primary winding, and it seems to be staying put.
I then connected everything up
for a test. The entire circuit puts out 75 to 80kV at 31V in. I'm not sure why, when it used to do the same at only 22V in some weeks ago. I presume that this is because there are corona losses from the external wiring, but I'm not going to bother fighting it. 31V is just a 6s and a 3s lipo in series. I'm probably going to buy a 3000mAh lipos, they should provide me with 30 1 minute exposures which is more than plenty. I'm not buying the lipos until I get the linear regulator done, and that is on this week's to-do list.
Some sparking next to an m&m at full power. It hurts my ears. EDIT 4got the video
As for the tube, I got the feedthroughs made, now I need to figure out how to insulate the HV feedthrough from the lead container. I'm thinking a PVC tube and loads of hot glue.
As for the tube I've been playing with the heater, and it definitely doesn't need many volts to get hot. Here is a "hotness chart"
I have prepared just by looking at the light. I'm going to limit it at 2V which should give me 2.5 or so mA of anode current.Some heater pics
@1.5V
@2V
And after all of these modifications there is no more leaking :D
Re: Grenadier's big thread of Röntgen related shenanigans
Freitsu, Tue Mar 22 2011, 10:19AM
Nice to see the progress on your project Grenadier!
You'll be taking radiographs in notime...
OT: did you get those tubes?
Freitsu, Tue Mar 22 2011, 10:19AM
Nice to see the progress on your project Grenadier!
You'll be taking radiographs in notime...
OT: did you get those tubes?
Re: Grenadier's big thread of Röntgen related shenanigans
Proud Mary, Tue Mar 22 2011, 05:16PM
I have no anode heating and cooling curves for dental tubes to look at, but would be concerned that a one minute exposure as you mention above could well exceed the heat capacity of the anode, and so cause irreversible damage. General purpose dental X-ray tubes are designed with exposures of less than one second in mind.
Heat capacity is exceeded when the rate of heat input to the anode exceeds the rate at which it can be dissipated, and is one of the key parameters of any X-ray tube.
Running the tube at reduced anode current - as you suggest - may perhaps be sufficient to keep the tube from overheating in long exposures, but you should investigate the anode heating and cooling cycle before committing to anything that might ruin it.
Proud Mary, Tue Mar 22 2011, 05:16PM
I have no anode heating and cooling curves for dental tubes to look at, but would be concerned that a one minute exposure as you mention above could well exceed the heat capacity of the anode, and so cause irreversible damage. General purpose dental X-ray tubes are designed with exposures of less than one second in mind.
Heat capacity is exceeded when the rate of heat input to the anode exceeds the rate at which it can be dissipated, and is one of the key parameters of any X-ray tube.
Running the tube at reduced anode current - as you suggest - may perhaps be sufficient to keep the tube from overheating in long exposures, but you should investigate the anode heating and cooling cycle before committing to anything that might ruin it.
Re: Grenadier's big thread of Röntgen related shenanigans
James, Tue Mar 22 2011, 06:04PM
There's a heating chart in the Kodak 2200 manual linked in here
This is for a Trophy TRX708 dental tube which is among the smallest I'm aware of. Max filament voltage is around 4.6V in most dental tubes, which ought to give you somewhere between 7-10 mA. If you run it at a low current like 2-3 mA the heat load on the anode will be substantially lower and the filament will last a lot longer at low temperature as well. At full output it will glow brightly like a normal tungsten light bulb.
James, Tue Mar 22 2011, 06:04PM
There's a heating chart in the Kodak 2200 manual linked in here
This is for a Trophy TRX708 dental tube which is among the smallest I'm aware of. Max filament voltage is around 4.6V in most dental tubes, which ought to give you somewhere between 7-10 mA. If you run it at a low current like 2-3 mA the heat load on the anode will be substantially lower and the filament will last a lot longer at low temperature as well. At full output it will glow brightly like a normal tungsten light bulb.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Tue Mar 22 2011, 07:28PM
Here is the tube data proud mary The anode heat storage capacity is 7kJ
Adam Munich, Tue Mar 22 2011, 07:28PM
Here is the tube data proud mary
The anode heat storage capacity is 7kJRe: Grenadier's big thread of Röntgen related shenanigans
Proud Mary, Tue Mar 22 2011, 08:10PM
Brilliant! Hangzhou Wandong Electron Co have made things easy by giving the maximum continuous power - 110W.
This would mean a maximum current of 1.47mA from a 75kV constant voltage supply. I'd say go with a bit less, because it's always best to be on
the conservative side where expensive parts are concerned.
With 75kV/1.25mA you will be getting somewhere between 25 - 30 Gy/hr at 30cm from the anode across the whole beam cone.
Proud Mary, Tue Mar 22 2011, 08:10PM
Grenadier wrote ...
Here is the tube data proud mary The anode heat storage capacity is 7kJ
Here is the tube data proud mary
The anode heat storage capacity is 7kJBrilliant! Hangzhou Wandong Electron Co have made things easy by giving the maximum continuous power - 110W.
This would mean a maximum current of 1.47mA from a 75kV constant voltage supply. I'd say go with a bit less, because it's always best to be on
the conservative side where expensive parts are concerned.
With 75kV/1.25mA you will be getting somewhere between 25 - 30 Gy/hr at 30cm from the anode across the whole beam cone.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Tue Mar 22 2011, 09:43PM
Well the CW is certainly capable of making 1.5mA, and 30Gy/hr is certainly enough x-radiation for me. The tube will also be under oil to help suck away some heat.
I need to figure out how to mount the tube in that tupperware w/o using any glue. Maybe some sort of foamboard contraption could do that.
Adam Munich, Tue Mar 22 2011, 09:43PM
Well the CW is certainly capable of making 1.5mA, and 30Gy/hr is certainly enough x-radiation for me. The tube will also be under oil to help suck away some heat.
I need to figure out how to mount the tube in that tupperware w/o using any glue. Maybe some sort of foamboard contraption could do that.
Re: Grenadier's big thread of Röntgen related shenanigans
Proud Mary, Tue Mar 22 2011, 11:15PM
There are various types of metal pipe clips and clamps you could use if you pad them with glass cloth, and don't over-tighten them.
If you don't want to use metal at all, you could simply wrap the tube fairly loosely with coarse glass cloth, or rock wool, leaving a hole over the exit window, and agitate it so the dielectric oil penetrates all way through it.
You could carve a support yoke out of refractory materials like brick. Or you could cast supports out of Plaster of Paris, fire cement, or even concrete, again padding the contact surfaces with glass cloth or rock wool.
Proud Mary, Tue Mar 22 2011, 11:15PM
Grenadier wrote ...
I need to figure out how to mount the tube in that tupperware w/o using any glue. Maybe some sort of foamboard contraption could do that.
I need to figure out how to mount the tube in that tupperware w/o using any glue. Maybe some sort of foamboard contraption could do that.
There are various types of metal pipe clips and clamps you could use if you pad them with glass cloth, and don't over-tighten them.
If you don't want to use metal at all, you could simply wrap the tube fairly loosely with coarse glass cloth, or rock wool, leaving a hole over the exit window, and agitate it so the dielectric oil penetrates all way through it.
You could carve a support yoke out of refractory materials like brick. Or you could cast supports out of Plaster of Paris, fire cement, or even concrete, again padding the contact surfaces with glass cloth or rock wool.
Re: Grenadier's big thread of Röntgen related shenanigans
James, Tue Mar 22 2011, 11:28PM
Get some styrene (sheets, not the foam), polycarbonate, acrylic, etc and fabricate a bracket for it that fits snugly in the housing. I get this sort of stuff from Tap Plastics as they have a bin of cutoffs they sell by the pound but you can get it other places too. The dental heads I've opened up had the tube bolted to a plastic mount by way of a bolt into a threaded hole in the anode stud and I suspect most are set up similarly.
If I were gonna try to mount a tube in my own housing, I think I'd get some plastic pipe and cut a disk out of plastic to stick over each end of the tube that fit into the pipe. Use threaded cleanout fittings for the ends and seal the wires through them, and drill & tap a small port through which to top off the oil. Wrap the outside of the pipe with lead sheet of sufficient thickness with a hole for the beam exit and then mount that whole assembly into a housing of some sort to protect the shielding.
It is WELL worth it to pick up an ion chamber survey meter if you are going to play with this stuff. Eberline makes some nice ones, as do others. Those cold war era Victoreen ones from the civil defense program are NOT sensitive enough. Probably cost you a couple hundred bucks for a decent used one but it's cheaper than cancer. Do NOT skimp on shielding or safety in general. Even more important than protecting yourself is ensuring that you don't expose anyone else to radiation. It is invisible, can scatter, and undeniably hazardous.
James, Tue Mar 22 2011, 11:28PM
Grenadier wrote ...
Well the CW is certainly capable of making 1.5mA, and 30Gy/hr is certainly enough x-radiation for me. The tube will also be under oil to help suck away some heat.
I need to figure out how to mount the tube in that tupperware w/o using any glue. Maybe some sort of foamboard contraption could do that.
Well the CW is certainly capable of making 1.5mA, and 30Gy/hr is certainly enough x-radiation for me. The tube will also be under oil to help suck away some heat.
I need to figure out how to mount the tube in that tupperware w/o using any glue. Maybe some sort of foamboard contraption could do that.
Get some styrene (sheets, not the foam), polycarbonate, acrylic, etc and fabricate a bracket for it that fits snugly in the housing. I get this sort of stuff from Tap Plastics as they have a bin of cutoffs they sell by the pound but you can get it other places too. The dental heads I've opened up had the tube bolted to a plastic mount by way of a bolt into a threaded hole in the anode stud and I suspect most are set up similarly.
If I were gonna try to mount a tube in my own housing, I think I'd get some plastic pipe and cut a disk out of plastic to stick over each end of the tube that fit into the pipe. Use threaded cleanout fittings for the ends and seal the wires through them, and drill & tap a small port through which to top off the oil. Wrap the outside of the pipe with lead sheet of sufficient thickness with a hole for the beam exit and then mount that whole assembly into a housing of some sort to protect the shielding.
It is WELL worth it to pick up an ion chamber survey meter if you are going to play with this stuff. Eberline makes some nice ones, as do others. Those cold war era Victoreen ones from the civil defense program are NOT sensitive enough. Probably cost you a couple hundred bucks for a decent used one but it's cheaper than cancer. Do NOT skimp on shielding or safety in general. Even more important than protecting yourself is ensuring that you don't expose anyone else to radiation. It is invisible, can scatter, and undeniably hazardous.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Tue Mar 22 2011, 11:33PM
Well I don't have a couple hundred dollars to spend on a survey meter...
I do have 7mm of lead shielding, and I'll be standing quite a distance away from it, so that should be plenty to reduce the dose-rate to nearly nothing. I am going to get a dosimeter too.
As for the plastic pipe idea, I already made a lead shield that conforms to a piece of tupperware so I can't really do much but work with what I've got right now.
Adam Munich, Tue Mar 22 2011, 11:33PM
Well I don't have a couple hundred dollars to spend on a survey meter...
I do have 7mm of lead shielding, and I'll be standing quite a distance away from it, so that should be plenty to reduce the dose-rate to nearly nothing. I am going to get a dosimeter too.
As for the plastic pipe idea, I already made a lead shield that conforms to a piece of tupperware so I can't really do much but work with what I've got right now.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Fri Mar 25 2011, 02:50AM
Mostly mechanical stuff today, just built the tube holder.
Smile!
Eventually I'll replace the canola oil with something inorganic, but this works for now. The x-rays need to transverse 1cm of oil, and although that will attenuate the beam I don't think it'll have very much effect. My biggest concern is that the tube will flashover under oil, and that is why I left the limiting resistor in the CW. W/o it a flashover = dead diodes. In order to flash over the HV would need to transverse about 4cm of oil, and at 75kV that is unlikely to happen (i hope).
I've been thinking about the tube heater and I was considering a linear voltage regulator, a low dropout one. Running off of 2 alkaline cells there is no chance that the tube's heater can be overvolted if the Vreg fails, though I am concerned about the reliability of such a regulator when it comes to electrostatics. I'm not so sure I'll have any room for D cells, so I may have to use C cells.
I was looking at the discharge curves of Lipos and it appears that I'll need a 10s lipo to compensate for voltage drop. I plan on using an LM317 and a TIP122 as a pass transistor, and that should give me about 8A of regulated current. I'll need a beefy heatsink, but since it is not running continuous duty heating shouldn't be too big of a problem, even if something like 40W of heat are being made when the kVp is lowered to 50kV. Eventually I plan on going the switch mode route, but meh this is good enough for now.
There was something else I was going to say but I seem to have forgotten it. Oh well.
Edit:
Now I remember, I need to cut holes in the Pb sheild and make the anode's HV feed through. I'm thinking a bic pen and a zillion pounds of hot glue could work.
Adam Munich, Fri Mar 25 2011, 02:50AM
Mostly mechanical stuff today, just built the tube holder.
Smile!
Eventually I'll replace the canola oil with something inorganic, but this works for now. The x-rays need to transverse 1cm of oil, and although that will attenuate the beam I don't think it'll have very much effect. My biggest concern is that the tube will flashover under oil, and that is why I left the limiting resistor in the CW. W/o it a flashover = dead diodes. In order to flash over the HV would need to transverse about 4cm of oil, and at 75kV that is unlikely to happen (i hope).
I've been thinking about the tube heater and I was considering a linear voltage regulator, a low dropout one. Running off of 2 alkaline cells there is no chance that the tube's heater can be overvolted if the Vreg fails, though I am concerned about the reliability of such a regulator when it comes to electrostatics. I'm not so sure I'll have any room for D cells, so I may have to use C cells.
I was looking at the discharge curves of Lipos and it appears that I'll need a 10s lipo to compensate for voltage drop. I plan on using an LM317 and a TIP122 as a pass transistor, and that should give me about 8A of regulated current. I'll need a beefy heatsink, but since it is not running continuous duty heating shouldn't be too big of a problem, even if something like 40W of heat are being made when the kVp is lowered to 50kV. Eventually I plan on going the switch mode route, but meh this is good enough for now.
There was something else I was going to say but I seem to have forgotten it. Oh well.
Edit:
Now I remember, I need to cut holes in the Pb sheild and make the anode's HV feed through. I'm thinking a bic pen and a zillion pounds of hot glue could work.
Re: Grenadier's big thread of Röntgen related shenanigans
klugesmith, Fri Mar 25 2011, 04:17AM
I've been thinking about regulated battery-powered filament supplies.
If the battery is a nominal 3.7-volt Li-ion type, then there isn't much
voltage headroom. With just a rheostat to control the filament power,
anode current will be -very- sensitive to battery voltage.
Here's an undeveloped concept: a low-dropout Current regulator,
which is easy on the filament when switched on.
I think it'll be easy to make one for (say) 2 amps, with dropout
voltage less than 200 mV (100 mV for sense R and 100 mV for the pass transistor).
Anybody here already done that, with part numbers & stable feedback?
klugesmith, Fri Mar 25 2011, 04:17AM
I've been thinking about regulated battery-powered filament supplies.
If the battery is a nominal 3.7-volt Li-ion type, then there isn't much
voltage headroom. With just a rheostat to control the filament power,
anode current will be -very- sensitive to battery voltage.
Here's an undeveloped concept: a low-dropout Current regulator,
which is easy on the filament when switched on.
I think it'll be easy to make one for (say) 2 amps, with dropout
voltage less than 200 mV (100 mV for sense R and 100 mV for the pass transistor).
Anybody here already done that, with part numbers & stable feedback?
Re: Grenadier's big thread of Röntgen related shenanigans
uzzors2k, Fri Mar 25 2011, 09:09AM
Scaling up to 2A shouldn't be hard, just make sure your op-amp can work down to ground if you choose a low sense resistor voltage.
uzzors2k, Fri Mar 25 2011, 09:09AM
Klugesmith wrote ...
Anybody here already done that, with part numbers & stable feedback?
Yeah. Anybody here already done that, with part numbers & stable feedback?
Scaling up to 2A shouldn't be hard, just make sure your op-amp can work down to ground if you choose a low sense resistor voltage.Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Fri Mar 25 2011, 12:22PM
So I was thinking this could possibly work. The two diodes are used to create a reference voltage while the op amp & resistive divider regulate&adjust stuff.
Adam Munich, Fri Mar 25 2011, 12:22PM
So I was thinking this could possibly work. The two diodes are used to create a reference voltage while the op amp & resistive divider regulate&adjust stuff.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Sat Mar 26 2011, 04:42AM
Today I built the high power linear regulator. I used a 2SA1943 PNP transistor to pass most of the current and it works very well. The heatsink gets only a couple of degrees above ambient even when the regulator drops 10V @ 5.5A, so that's good.
The regulator has a relatively high dropout of 2.9V so the 10s lipo will still work for giving the CW 31V. Most of the battery's discharge curve will be at 35v so that leaves 33v for the CW when the regulator isn't uhh, "in use".
Adam Munich, Sat Mar 26 2011, 04:42AM
Today I built the high power linear regulator.
I used a 2SA1943 PNP transistor to pass most of the current and it works very well. The heatsink gets only a couple of degrees above ambient even when the regulator drops 10V @ 5.5A, so that's good.The regulator has a relatively high dropout of 2.9V so the 10s lipo will still work for giving the CW 31V. Most of the battery's discharge curve will be at 35v so that leaves 33v for the CW when the regulator isn't uhh, "in use".
Re: Grenadier's big thread of Röntgen related shenanigans
Inducktion, Sat Mar 26 2011, 06:56PM
Is that a CPU heatsink? How did you cut the holes for the screws? I still can't figure out how to do it.
Inducktion, Sat Mar 26 2011, 06:56PM
Grenadier wrote ...
Today I built the high power linear regulator. I used a 2SA1943 PNP transistor to pass most of the current and it works very well. The heatsink gets only a couple of degrees above ambient even when the regulator drops 10V @ 5.5A, so that's good.
The regulator has a relatively high dropout of 2.9V so the 10s lipo will still work for giving the CW 31V. Most of the battery's discharge curve will be at 35v so that leaves 33v for the CW when the regulator isn't uhh, "in use".
Today I built the high power linear regulator.
I used a 2SA1943 PNP transistor to pass most of the current and it works very well. The heatsink gets only a couple of degrees above ambient even when the regulator drops 10V @ 5.5A, so that's good.The regulator has a relatively high dropout of 2.9V so the 10s lipo will still work for giving the CW 31V. Most of the battery's discharge curve will be at 35v so that leaves 33v for the CW when the regulator isn't uhh, "in use".
Is that a CPU heatsink? How did you cut the holes for the screws? I still can't figure out how to do it.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Mon Apr 04 2011, 12:53AM
So the past week has been nothing but fail when it comes to woodworking.
First I sanded the boxes, and they looked good: until I stained them. The stain went on uneven and wouldn't get dark. After trying again and again to darken it I then asked HVCOMM what finish would be best. I suggested acrylic but NOOOO! use shellac.
So I bought a can of spray on shellac and put it on: it ran. Then after it was dry I picked it up and dry after 24 hours my ass! Fast forward a week and 7 more tries and it still looks like ass. A week and $20 wasted. Gah I'm pissed.
I'm just going to get new boxes and try again; it'll be cheaper anyway.
Adam Munich, Mon Apr 04 2011, 12:53AM
So the past week has been nothing but fail when it comes to woodworking.
First I sanded the boxes, and they looked good: until I stained them. The stain went on uneven and wouldn't get dark. After trying again and again to darken it I then asked HVCOMM what finish would be best. I suggested acrylic but NOOOO! use shellac.
So I bought a can of spray on shellac and put it on: it ran. Then after it was dry I picked it up and dry after 24 hours my ass! Fast forward a week and 7 more tries and it still looks like ass. A week and $20 wasted. Gah I'm pissed.
I'm just going to get new boxes and try again; it'll be cheaper anyway.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Thu Apr 07 2011, 03:43AM
I got my meters in the mail the other day a 50uA meter for measuring anode voltage and a 3mA meter for measuring anode current. I have no pics yet, though I will tomorrow.
In series with the 50uA meter is a 1.8G resistor, and that turns it into a 90kV meter. Below 40kV there is no problems with measurement, but anything above and all hell breaks loose inside the meter. The needle starts swinging back and forth at a million miles an hour presumably due to electrostatics. When the CW is allowed to spark this problem is greatly reduced, yet not entirely eliminated. Nonetheless the meter seems to check out ok when it comes to measurement, so that's a good sign.
Although the meter works when the CW is allowed to spark, I am wondering about what will happen when there is an x-ray tube in the way. An x-ray tube is not really a short circuit like a spark is, so I am concerned that the electrostatics will once again reap havoc on the meter. The question is, will the tube appear as a high resistance load on the CW? If so then electrostatics will be a huge issue. If ohm's law fits the situation then it should appear as a 25 meg resistor if 3mA gets through at 75kV...
Wat do.
Adam Munich, Thu Apr 07 2011, 03:43AM
I got my meters in the mail the other day a 50uA meter for measuring anode voltage and a 3mA meter for measuring anode current. I have no pics yet, though I will tomorrow.
In series with the 50uA meter is a 1.8G resistor, and that turns it into a 90kV meter. Below 40kV there is no problems with measurement, but anything above and all hell breaks loose inside the meter. The needle starts swinging back and forth at a million miles an hour presumably due to electrostatics. When the CW is allowed to spark this problem is greatly reduced, yet not entirely eliminated. Nonetheless the meter seems to check out ok when it comes to measurement, so that's a good sign.
Although the meter works when the CW is allowed to spark, I am wondering about what will happen when there is an x-ray tube in the way. An x-ray tube is not really a short circuit like a spark is, so I am concerned that the electrostatics will once again reap havoc on the meter. The question is, will the tube appear as a high resistance load on the CW? If so then electrostatics will be a huge issue. If ohm's law fits the situation then it should appear as a 25 meg resistor if 3mA gets through at 75kV...
Wat do.
Re: Grenadier's big thread of Röntgen related shenanigans
Proud Mary, Thu Apr 07 2011, 08:20AM
Do you have the negative lug of the 50μA meter tied to Earth, and the positive to your 1.8G resistor?
What is the voltage rating of this resistor?
It's never a good idea to run a C&W without a load.
It's perfectly valid to think of an X-ray tube as a somewhat non-linear resistor in series with a diode. It will pull down your voltage quite a lot, so measure the voltage directly across the tube so you can be sure you know what is going on.
Wire a gas arrestor or small neon directly across the meter terminals to stop the whole thing going live if the meter should fail open circuit.
Proud Mary, Thu Apr 07 2011, 08:20AM
Do you have the negative lug of the 50μA meter tied to Earth, and the positive to your 1.8G resistor?
What is the voltage rating of this resistor?
It's never a good idea to run a C&W without a load.
It's perfectly valid to think of an X-ray tube as a somewhat non-linear resistor in series with a diode. It will pull down your voltage quite a lot, so measure the voltage directly across the tube so you can be sure you know what is going on.
Wire a gas arrestor or small neon directly across the meter terminals to stop the whole thing going live if the meter should fail open circuit.
Re: Grenadier's big thread of Röntgen related shenanigans
uzzors2k, Thu Apr 07 2011, 03:21PM
Is your meter plastic like this one? I have the exact same problem with my meter, at roughly the same voltage. My setup consists of a 1G resistor made up of five 200M ones in series. These have been placed in a PVC pipe and encased in wax. I thought the meter jumping was caused by arc-overs in my 1G resistor, but perhaps it's something else. I'm sure it's not electrostatics, as that only caused slow deflections on a different meter (metal) during my first x-ray experiments. I should also add, during my first x-ray experiments I used the same 1G resistor but it was sealed with oil, and I used a voltmeter in series with a smaller 1.1M resistor. No problems then, so I'll try reverting back to this setup.
Try making a resistor divider with your 1.8G resistor and measure voltage instead. If that doesn't work any better check if it's arcing-over somewhere. With 50µA sensitivity it won't take much to peg the meter.
uzzors2k, Thu Apr 07 2011, 03:21PM
Is your meter plastic like this one?
I have the exact same problem with my meter, at roughly the same voltage. My setup consists of a 1G resistor made up of five 200M ones in series. These have been placed in a PVC pipe and encased in wax. I thought the meter jumping was caused by arc-overs in my 1G resistor, but perhaps it's something else. I'm sure it's not electrostatics, as that only caused slow deflections on a different meter (metal) during my first x-ray experiments. I should also add, during my first x-ray experiments I used the same 1G resistor but it was sealed with oil, and I used a voltmeter in series with a smaller 1.1M resistor. No problems then, so I'll try reverting back to this setup.Try making a resistor divider with your 1.8G resistor and measure voltage instead. If that doesn't work any better check if it's arcing-over somewhere. With 50µA sensitivity it won't take much to peg the meter.
Re: Grenadier's big thread of Röntgen related shenanigans
James, Thu Apr 07 2011, 06:01PM
I used a switching regulator I build with a LM2576 set to about 4.2V. If you are worried about damaging the filament, make a crowbar circuit out of an SCR and 5V zener diode so that the SCR latches and shorts across the output if the voltage exceeds the zener breakdown. The problem with batteries is that they wear down quickly and your filament current dips.
You can get nice clear mineral oil easily, it's sold as a laxative for both humans and animals. I originally was getting small bottles at the pharmacy but then I found agricultural supply shops sell it in gallon and larger jugs meant for livestock. If you have problems with flashover you may need to find someone with a vacuum pump and chamber to degass the oil as it absorbs moisture and other gases.
James, Thu Apr 07 2011, 06:01PM
I used a switching regulator I build with a LM2576 set to about 4.2V. If you are worried about damaging the filament, make a crowbar circuit out of an SCR and 5V zener diode so that the SCR latches and shorts across the output if the voltage exceeds the zener breakdown. The problem with batteries is that they wear down quickly and your filament current dips.
You can get nice clear mineral oil easily, it's sold as a laxative for both humans and animals. I originally was getting small bottles at the pharmacy but then I found agricultural supply shops sell it in gallon and larger jugs meant for livestock. If you have problems with flashover you may need to find someone with a vacuum pump and chamber to degass the oil as it absorbs moisture and other gases.
Re: Grenadier's big thread of Röntgen related shenanigans
Proud Mary, Thu Apr 07 2011, 08:14PM
I haven't experienced this problem myself, as yet. I use combinations of Enersys Cyclon 2V 8AH lead-acid cells and NiMH 1.2V 9AH cells, and find they stand up very well for a couple of hours supplying heater current of an amp or two - perhaps the simplest solution to the need for a floating heater supply when using a grounded anode X-ray tube.
The XRD and XRF tubes I use are designed to be operated for hours at a time without overheating, if need be. But if you are using diagnostic radiography tubes - dental types for example - the tube will be destroyed by overheating long before the heater batteries run out.
Proud Mary, Thu Apr 07 2011, 08:14PM
James wrote ...
The problem with batteries is that they wear down quickly and your filament current dips.
The problem with batteries is that they wear down quickly and your filament current dips.
I haven't experienced this problem myself, as yet. I use combinations of Enersys Cyclon 2V 8AH lead-acid cells and NiMH 1.2V 9AH cells, and find they stand up very well for a couple of hours supplying heater current of an amp or two - perhaps the simplest solution to the need for a floating heater supply when using a grounded anode X-ray tube.
The XRD and XRF tubes I use are designed to be operated for hours at a time without overheating, if need be. But if you are using diagnostic radiography tubes - dental types for example - the tube will be destroyed by overheating long before the heater batteries run out.
Re: Grenadier's big thread of Röntgen related shenanigans
James, Thu Apr 07 2011, 09:11PM
The issue I saw was not so much the batteries wearing down completely, but that the output would always sag a bit. Do a dozen consecutive exposures at say 0.75sec each and the first couple come out overexposed, the next few are perfect, and the last ones underexposed. It may vary by tube though, perhaps some give a much larger change in anode current for the change in filament voltage. Regardless of the power source, a regulator is a big improvement.
James, Thu Apr 07 2011, 09:11PM
The issue I saw was not so much the batteries wearing down completely, but that the output would always sag a bit. Do a dozen consecutive exposures at say 0.75sec each and the first couple come out overexposed, the next few are perfect, and the last ones underexposed. It may vary by tube though, perhaps some give a much larger change in anode current for the change in filament voltage. Regardless of the power source, a regulator is a big improvement.
Re: Grenadier's big thread of Röntgen related shenanigans
Proud Mary, Thu Apr 07 2011, 09:36PM
Have you thought this through? Your 12*0.75 sec exposures at say 2A using the 2V 8 AH Cyclon lead-acid cells I recommended will require 18 C out of the 28800 C ideally stored in the cell - a loss of 0.0625% of the charge available.
In any event, I don't see any reason why Grenadier would want to work in grounded anode mode with a dental tube, so the problem of providing a floating filament supply with a high stand-off voltage will not arise.
Proud Mary, Thu Apr 07 2011, 09:36PM
James wrote ...
The issue I saw was not so much the batteries wearing down completely, but that the output would always sag a bit. Do a dozen consecutive exposures at say 0.75sec each and the first couple come out overexposed, the next few are perfect, and the last ones underexposed. It may vary by tube though, perhaps some give a much larger change in anode current for the change in filament voltage. Regardless of the power source, a regulator is a big improvement.
The issue I saw was not so much the batteries wearing down completely, but that the output would always sag a bit. Do a dozen consecutive exposures at say 0.75sec each and the first couple come out overexposed, the next few are perfect, and the last ones underexposed. It may vary by tube though, perhaps some give a much larger change in anode current for the change in filament voltage. Regardless of the power source, a regulator is a big improvement.
Have you thought this through? Your 12*0.75 sec exposures at say 2A using the 2V 8 AH Cyclon lead-acid cells I recommended will require 18 C out of the 28800 C ideally stored in the cell - a loss of 0.0625% of the charge available.
In any event, I don't see any reason why Grenadier would want to work in grounded anode mode with a dental tube, so the problem of providing a floating filament supply with a high stand-off voltage will not arise.
Re: Grenadier's big thread of Röntgen related shenanigans
James, Fri Apr 08 2011, 12:20AM
This was a dental tube, grounded cathode, so that wasn't an issue. I was using NiMH cells, not SLA as it was what was on hand, and they did sag over time. It's been a while since I've messed with SLA since they always seem to be dead by the time I need them. LM2576 works just great though, it can run from the same 15V supply that powers the mosfet driver, runs cool and efficient, and the voltage stays put.
James, Fri Apr 08 2011, 12:20AM
This was a dental tube, grounded cathode, so that wasn't an issue. I was using NiMH cells, not SLA as it was what was on hand, and they did sag over time. It's been a while since I've messed with SLA since they always seem to be dead by the time I need them. LM2576 works just great though, it can run from the same 15V supply that powers the mosfet driver, runs cool and efficient, and the voltage stays put.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Fri Apr 08 2011, 05:12AM
After an hour of WTF (things weren't obeying ohm's law) I realized the millameter wasn't mesuring right (too sensitive). Turns out the 100 year old shunt resistor was 109 ohms; 'twas supposed to be 3.4. So... I took couple feet of 39ga and made a new shunt. 23.5v through a 10k resistor ought to give 2.3mA, the meter now says 2.3mA so that's one problem solved.
Now here's another issue; with a 20 meg resistor as a load the CW supplies 2.5mA at 5kV (supposed to be 35-40kV). The resistor burned up in a hurry (it's only 1/4W) but that's still not right; it's a huge drop. I think the problem might be the 15 meg current limiting resistor I put in there. If I do remove it (I'll probably have to) I'll have to make certain I don't let the CW spark where it's not supposed to or else it's curtains for the 20mA diodes.
Seeing as I don't have a 20 meg 300 something watt resistor to use as a dummy x-ray tube it looks like I'll have to just test the circuit using the coolidge tube. By putting it in my backyard and having the tube inside of that big 1cm thick lead box I made before, and by powering up the circuit remotely I should be safe. I could use my video camera to monitor the meters and see if things work all right. I really don't need more than 1mA out of the CW, but theoretically I should be getting only 1.6kV drop per mA:
(0.001 / (60,000 * 5e-10) * (((2 / 3) * (4^3)) + ((4^2) / 2) - (4 / 6)) = 1 666.666666666666666
Another problem, there is a little bit of tiny arcing inside the mA meter. The coil is arcing to the magnet inside, though it can't be more than a few uA in that arc. There might be something I can do there to solve that.
Pic of the meters they are bakelite while the faces are metal and the windows are glass. For some odd reason the swinging problem on the kilovoltmeter stopped, so that's good.
Adam Munich, Fri Apr 08 2011, 05:12AM
After an hour of WTF (things weren't obeying ohm's law) I realized the millameter wasn't mesuring right (too sensitive). Turns out the 100 year old shunt resistor was 109 ohms; 'twas supposed to be 3.4. So... I took couple feet of 39ga and made a new shunt. 23.5v through a 10k resistor ought to give 2.3mA, the meter now says 2.3mA so that's one problem solved.
Now here's another issue; with a 20 meg resistor as a load the CW supplies 2.5mA at 5kV (supposed to be 35-40kV). The resistor burned up in a hurry (it's only 1/4W) but that's still not right; it's a huge drop. I think the problem might be the 15 meg current limiting resistor I put in there. If I do remove it (I'll probably have to) I'll have to make certain I don't let the CW spark where it's not supposed to or else it's curtains for the 20mA diodes.
Seeing as I don't have a 20 meg 300 something watt resistor to use as a dummy x-ray tube it looks like I'll have to just test the circuit using the coolidge tube. By putting it in my backyard and having the tube inside of that big 1cm thick lead box I made before, and by powering up the circuit remotely I should be safe. I could use my video camera to monitor the meters and see if things work all right. I really don't need more than 1mA out of the CW, but theoretically I should be getting only 1.6kV drop per mA:
(0.001 / (60,000 * 5e-10) * (((2 / 3) * (4^3)) + ((4^2) / 2) - (4 / 6)) = 1 666.666666666666666
Another problem, there is a little bit of tiny arcing inside the mA meter. The coil is arcing to the magnet inside, though it can't be more than a few uA in that arc. There might be something I can do there to solve that.
Pic of the meters
they are bakelite while the faces are metal and the windows are glass. For some odd reason the swinging problem on the kilovoltmeter stopped, so that's good.Re: Grenadier's big thread of Röntgen related shenanigans
Proud Mary, Fri Apr 08 2011, 08:44AM
OK, so the voltage drop across your 15MΩ current limiting resistor when 2.5mA is flowing is:
V = IR
V = 0.0025A * 15000000Ω
= 37,500V
As W = VI
= 37500V*0.0025A
= 93.75W - almost 100W gone up in smoke, with nothing to show for it!
Now, to do away with the 15MΩ resistance and not risk flashover, you should supply filament current to the X-ray tube a good 3 min before you supply the HV. This will ensure that the tube conducts at once when high voltage is supplied, which will pull the supply down to a safe value before it can get up to any mischief.
If you would post up a schematic of the whole setup showing where you have put the meters, and any shunts or droppers that you may have wired up to them, we can see what else can be done to sort all this out.
Proud Mary, Fri Apr 08 2011, 08:44AM
Grenadier wrote ...
Now here's another issue; with a 20 meg resistor as a load the CW supplies 2.5mA at 5kV (supposed to be 35-40kV). The resistor burned up in a hurry (it's only 1/4W) but that's still not right; it's a huge drop. I think the problem might be the 15 meg current limiting resistor I put in there. If I do remove it (I'll probably have to) I'll have to make certain I don't let the CW spark where it's not supposed to or else it's curtains for the 20mA diodes.
Now here's another issue; with a 20 meg resistor as a load the CW supplies 2.5mA at 5kV (supposed to be 35-40kV). The resistor burned up in a hurry (it's only 1/4W) but that's still not right; it's a huge drop. I think the problem might be the 15 meg current limiting resistor I put in there. If I do remove it (I'll probably have to) I'll have to make certain I don't let the CW spark where it's not supposed to or else it's curtains for the 20mA diodes.
OK, so the voltage drop across your 15MΩ current limiting resistor when 2.5mA is flowing is:
V = IR
V = 0.0025A * 15000000Ω
= 37,500V
As W = VI
= 37500V*0.0025A
= 93.75W - almost 100W gone up in smoke, with nothing to show for it!
Now, to do away with the 15MΩ resistance and not risk flashover, you should supply filament current to the X-ray tube a good 3 min before you supply the HV. This will ensure that the tube conducts at once when high voltage is supplied, which will pull the supply down to a safe value before it can get up to any mischief.
If you would post up a schematic of the whole setup showing where you have put the meters, and any shunts or droppers that you may have wired up to them, we can see what else can be done to sort all this out.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Fri Apr 08 2011, 10:26AM
Hmm... I just found a bazillion 80K 2 watt resistors. If I put 250 in series that is a 20 meg 500W resistor (I think, morning math isn't so good). Looks like /i can in fact make a dummy tube.
I'll make a schematic today.
Adam Munich, Fri Apr 08 2011, 10:26AM
Hmm... I just found a bazillion 80K 2 watt resistors. If I put 250 in series that is a 20 meg 500W resistor (I think, morning math isn't so good). Looks like /i can in fact make a dummy tube.
I'll make a schematic today.
Re: Grenadier's big thread of Röntgen related shenanigans
Proud Mary, Fri Apr 08 2011, 01:51PM
It can be very helpful to run off a few large schematics that you can write comments on, and then tick off each connection in the construction only when you have physically checked it. You can note what voltage or current is supposed to be where, and in what coloured wire, and then check it off only when its presence has been verified. You can add number tags to each wire, which relate to numbered wires on the schematic. Many blunders can be avoided this way.
Proud Mary, Fri Apr 08 2011, 01:51PM
Grenadier wrote ...
Hmm... I just found a bazillion 80K 2 watt resistors. If I put 250 in series that is a 20 meg 500W resistor (I think, morning math isn't so good). Looks like /i can in fact make a dummy tube.
I'll make a schematic today.
Hmm... I just found a bazillion 80K 2 watt resistors. If I put 250 in series that is a 20 meg 500W resistor (I think, morning math isn't so good). Looks like /i can in fact make a dummy tube.
I'll make a schematic today.
It can be very helpful to run off a few large schematics that you can write comments on, and then tick off each connection in the construction only when you have physically checked it. You can note what voltage or current is supposed to be where, and in what coloured wire, and then check it off only when its presence has been verified. You can add number tags to each wire, which relate to numbered wires on the schematic. Many blunders can be avoided this way.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Sun Apr 10 2011, 02:39AM
Well I made the resistor, it's a little under 20 megohms.
I measured the voltage and current across it and at 36V into the zvs I get 65kV and 2.5mA through the HV side. Now there is a huge issue with loading, it's like 30kV per mA. This is definatley not right and I think it is due to huge corona losses on the large and pointy resistor string. I'm going to put it inside aquarium tube with oil and see if that helps. I also need a bigger resistor to test loading at lower currents.
Pics some other time.
Ugh, tired, can't put words together right. :p
Adam Munich, Sun Apr 10 2011, 02:39AM
Well I made the resistor, it's a little under 20 megohms.
I measured the voltage and current across it and at 36V into the zvs I get 65kV and 2.5mA through the HV side. Now there is a huge issue with loading, it's like 30kV per mA. This is definatley not right and I think it is due to huge corona losses on the large and pointy resistor string. I'm going to put it inside aquarium tube with oil and see if that helps. I also need a bigger resistor to test loading at lower currents.
Pics some other time.
Ugh, tired, can't put words together right. :p
Re: Grenadier's big thread of Röntgen related shenanigans
klugesmith, Mon Apr 11 2011, 07:17PM
klugesmith, Mon Apr 11 2011, 07:17PM
Grenadier wrote ...
I measured the voltage and current across it and at 36V into the zvs I get 65kV and 2.5mA through the HV side. Now there is a huge issue with loading, it's like 30kV per mA.
Sounds like the multiplier doesn't need improving. Good work! Now go make x-ray pictures!I measured the voltage and current across it and at 36V into the zvs I get 65kV and 2.5mA through the HV side. Now there is a huge issue with loading, it's like 30kV per mA.
Re: Grenadier's big thread of Röntgen related shenanigans
James, Mon Apr 11 2011, 08:42PM
Huge drops are typical of CW voltage multipliers. X ray heads that use these have closed loop regulation where the anode voltage is monitored through a high value resistor and used to control the power into the transformer to compensate for the loading.
You can get away with open loop if you're sure to always power the filament before turning on the HV. Fail to do that and it can easily shoot up over 100kV and arc.
James, Mon Apr 11 2011, 08:42PM
Huge drops are typical of CW voltage multipliers. X ray heads that use these have closed loop regulation where the anode voltage is monitored through a high value resistor and used to control the power into the transformer to compensate for the loading.
You can get away with open loop if you're sure to always power the filament before turning on the HV. Fail to do that and it can easily shoot up over 100kV and arc.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Mon Apr 11 2011, 11:58PM
meh... So I'm getting plenty of current, at 36V in I get 3mA out, yet only 60kV. Theoretically I should be getting only 1mA out with my 26 meg resistor but it would appear that I'm getting more.
It looks like the only way for me to see if it'll work is to hook it up to my coolidge tube and and see what happens. I have my 1cm thick pb box so that ought to stop near everything, so provided there is no rain I'll be hooking up the tube tonight.
I don't have an LDO regulator for my heater yet, so I'm just going to use a rheostat for the time being.
But first, I need a nap.
Adam Munich, Mon Apr 11 2011, 11:58PM
meh... So I'm getting plenty of current, at 36V in I get 3mA out, yet only 60kV. Theoretically I should be getting only 1mA out with my 26 meg resistor but it would appear that I'm getting more.
It looks like the only way for me to see if it'll work is to hook it up to my coolidge tube and and see what happens. I have my 1cm thick pb box so that ought to stop near everything, so provided there is no rain I'll be hooking up the tube tonight.
I don't have an LDO regulator for my heater yet, so I'm just going to use a rheostat for the time being.
But first, I need a nap.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Tue Apr 12 2011, 04:41AM
Alright 4HV, I present to you the latest and greatest in scientific prototyping ingenuity.
It works :D
As expected voltage is dependent on current and current on voltage, but with 1mA flowing through the tube the anode is at 65kV, while 24V is being fed into the device. That means a 32V lipo ought to work fine. Seeing as things are dependent on each other it might be hard to get consistent exposures, but that's what photoshop is for.
Now here's a problem I expected; scatter. Quite a lot actually. If I leave the GM tube outside, 12 feet behind the lead box it sounds like it's being held up to some fiestaware. Pressed right behind the lead box it clicks even faster. Concerned about this I took shelter behind my sliding glass door and the clicks dropped down dramatically; maybe a couple more per second over background. This means the scattered X-rays are soft, and the only explanation I have for that is bremsstrahlung. I still have enough lead sheet left to make a nice vest so I might be doing that in the future. Either that, or I could make it remote controlled. That kinda makes the meters pointless though... (unless I find a way to monitor kV/mA via an arduino, then I could simply tx the data to an LCD on the remote. I also managed to saturate the GM tube by putting it in the beam, that was pretty neat, and I fixed the unsteady-ness of the kilovoltmeter by putting the resistors under oil with the tube (pix to come)
And of course I couldn't call it a night without x-raying a few things.
A hard drive.
A pen I stole from my friend.
Adam Munich, Tue Apr 12 2011, 04:41AM
Alright 4HV, I present to you the latest and greatest in scientific prototyping ingenuity.
It works :D
As expected voltage is dependent on current and current on voltage, but with 1mA flowing through the tube the anode is at 65kV, while 24V is being fed into the device. That means a 32V lipo ought to work fine. Seeing as things are dependent on each other it might be hard to get consistent exposures, but that's what photoshop is for.
Now here's a problem I expected; scatter. Quite a lot actually. If I leave the GM tube outside, 12 feet behind the lead box it sounds like it's being held up to some fiestaware. Pressed right behind the lead box it clicks even faster. Concerned about this I took shelter behind my sliding glass door and the clicks dropped down dramatically; maybe a couple more per second over background. This means the scattered X-rays are soft, and the only explanation I have for that is bremsstrahlung. I still have enough lead sheet left to make a nice vest so I might be doing that in the future. Either that, or I could make it remote controlled. That kinda makes the meters pointless though... (unless I find a way to monitor kV/mA via an arduino, then I could simply tx the data to an LCD on the remote. I also managed to saturate the GM tube by putting it in the beam, that was pretty neat, and I fixed the unsteady-ness of the kilovoltmeter by putting the resistors under oil with the tube (pix to come)
And of course I couldn't call it a night without x-raying a few things.
A hard drive.
A pen I stole from my friend.
Re: Grenadier's big thread of Röntgen related shenanigans
Proud Mary, Tue Apr 12 2011, 12:38PM
Remember that if you have Va = 65 kV then less that 1% of your photons will be 65 keV. Most of them will be between ~15 - 30 keV, because the number of photons actually produced increases as photon energy decreases. About 0.03% of 30 keV X-ray photons will survive a journey of 100 yards through the air, and be easily detected.
So far as I understand your setup, the entire output of your tube will be bremsstrahlung, because W K-shell electrons have a binding energy of 69.5 keV. To kick any of these out, your bombarding electrons must have energies greater than 69.5keV i.e. in practice, you'd have to stick about 72 kV and more on the anode - hence the standard 75 kV dental tube.
When you succed in kicking out a tungsten K-shell electron, its hole will immediately be filled by an electron from the L-shell - binding energy 10.2 keV. The difference between these energy states - 69.5 keV and 10.2 keV - gives us the W characteristic X-ray photon energy 69.5 - 10.2 = 59.3 keV
Proud Mary, Tue Apr 12 2011, 12:38PM
Grenadier wrote ...
Now here's a problem I expected; scatter. Quite a lot actually. If I leave the GM tube outside, 12 feet behind the lead box it sounds like it's being held up to some fiestaware. Pressed right behind the lead box it clicks even faster. Concerned about this I took shelter behind my sliding glass door and the clicks dropped down dramatically; maybe a couple more per second over background. This means the scattered X-rays are soft, and the only explanation I have for that is bremsstrahlung. I still have enough lead sheet left to make a nice vest so I might be doing that in the future. Either that, or I could make it remote controlled. That kinda makes the meters pointless though... (unless I find a way to monitor kV/mA via an arduino, then I could simply tx the data to an LCD on the remote. I also managed to saturate the GM tube by putting it in the beam, that was pretty neat, and I fixed the unsteady-ness of the kilovoltmeter by putting the resistors under oil with the tube (pix to come)
Now here's a problem I expected; scatter. Quite a lot actually. If I leave the GM tube outside, 12 feet behind the lead box it sounds like it's being held up to some fiestaware. Pressed right behind the lead box it clicks even faster. Concerned about this I took shelter behind my sliding glass door and the clicks dropped down dramatically; maybe a couple more per second over background. This means the scattered X-rays are soft, and the only explanation I have for that is bremsstrahlung. I still have enough lead sheet left to make a nice vest so I might be doing that in the future. Either that, or I could make it remote controlled. That kinda makes the meters pointless though... (unless I find a way to monitor kV/mA via an arduino, then I could simply tx the data to an LCD on the remote. I also managed to saturate the GM tube by putting it in the beam, that was pretty neat, and I fixed the unsteady-ness of the kilovoltmeter by putting the resistors under oil with the tube (pix to come)
Remember that if you have Va = 65 kV then less that 1% of your photons will be 65 keV. Most of them will be between ~15 - 30 keV, because the number of photons actually produced increases as photon energy decreases. About 0.03% of 30 keV X-ray photons will survive a journey of 100 yards through the air, and be easily detected.
So far as I understand your setup, the entire output of your tube will be bremsstrahlung, because W K-shell electrons have a binding energy of 69.5 keV. To kick any of these out, your bombarding electrons must have energies greater than 69.5keV i.e. in practice, you'd have to stick about 72 kV and more on the anode - hence the standard 75 kV dental tube.
When you succed in kicking out a tungsten K-shell electron, its hole will immediately be filled by an electron from the L-shell - binding energy 10.2 keV. The difference between these energy states - 69.5 keV and 10.2 keV - gives us the W characteristic X-ray photon energy 69.5 - 10.2 = 59.3 keV
Re: Grenadier's big thread of Röntgen related shenanigans
radhoo, Tue Apr 12 2011, 03:06PM
congrats on your first results!
for your meters, you might be interested in getting one of those cheap Chinese wireless cameras, that broadcasts in 2.4GHz. Then you can watch your setup remotely on a TV. Otherwise it might be difficult integrating some sensitive digital measuring equipment into your HV circuit.
Other options: use a camera to photograph your instruments, triggered remotely or with a timer.
radhoo, Tue Apr 12 2011, 03:06PM
congrats on your first results!
for your meters, you might be interested in getting one of those cheap Chinese wireless cameras, that broadcasts in 2.4GHz. Then you can watch your setup remotely on a TV. Otherwise it might be difficult integrating some sensitive digital measuring equipment into your HV circuit.
Other options: use a camera to photograph your instruments, triggered remotely or with a timer.
Re: Grenadier's big thread of Röntgen related shenanigans
Xray, Tue Apr 12 2011, 03:55PM
X-rays do scatter. It's a nature of the beast, and there isn't much that you can do to mitigate all of it, short of lining your entire room with 10mm thick lead, and standing outside during exposure.
As you know, I repair dental X-ray heads for a living. I receive scattered X-rays to my body every time I energize a head for testing. When I first got into this business about 13 years ago, I bought a lead-lined vest, which I wore every time I needed to test a head. But I soon stopped wearing it because it was heavy and cumbersome, and the slight amount of scattered X-rays that I receive during each exposure is negligable (I of course avoid the main beam by standing behind the energized head). Using a standard GM Geiger Counter, I was measuring various intensities of radiation all around my shop (which is the size of a 2-car garage). No radiation extends beyond the walls, and so my neighbors have nothing to worry about. The bottom line is, most scattered radiation that I receive is low-energy, which probably doesn't penetrate my skin. Also, most test exposures last less than one second, and I typically make 3 or 4 test exposures (<1 second each) to make sure that the repaired head is operating within manufacturer's specifications. I check KVp, mA, and MR, as well as off-axis radiation.
In general, where safety is concerned, a person needs to be reasonably protected from the threat without being overly protected to the point where he/she can no longer function. So, should you wear a lead lined vest? Sure, so long as it doesn't become a burden, and if the threat of damage to your health is significant. If you are not certain about the risk, then it's better to be safe than sorry.
Xray, Tue Apr 12 2011, 03:55PM
Grenadier wrote ...
Now here's a problem I expected; scatter. Quite a lot actually. If I leave the GM tube outside, 12 feet behind the lead box it sounds like it's being held up to some fiestaware. Pressed right behind the lead box it clicks even faster. Concerned about this I took shelter behind my sliding glass door and the clicks dropped down dramatically; maybe a couple more per second over background. This means the scattered X-rays are soft, and the only explanation I have for that is bremsstrahlung. I still have enough lead sheet left to make a nice vest so I might be doing that in the future. Either that, or I could make it remote controlled. That kinda makes the meters pointless though... (unless I find a way to monitor kV/mA via an arduino, then I could simply tx the data to an LCD on the remote. I also managed to saturate the GM tube by putting it in the beam, that was pretty neat, and I fixed the unsteady-ness of the kilovoltmeter by putting the resistors under oil with the tube (pix to come)
Now here's a problem I expected; scatter. Quite a lot actually. If I leave the GM tube outside, 12 feet behind the lead box it sounds like it's being held up to some fiestaware. Pressed right behind the lead box it clicks even faster. Concerned about this I took shelter behind my sliding glass door and the clicks dropped down dramatically; maybe a couple more per second over background. This means the scattered X-rays are soft, and the only explanation I have for that is bremsstrahlung. I still have enough lead sheet left to make a nice vest so I might be doing that in the future. Either that, or I could make it remote controlled. That kinda makes the meters pointless though... (unless I find a way to monitor kV/mA via an arduino, then I could simply tx the data to an LCD on the remote. I also managed to saturate the GM tube by putting it in the beam, that was pretty neat, and I fixed the unsteady-ness of the kilovoltmeter by putting the resistors under oil with the tube (pix to come)
X-rays do scatter. It's a nature of the beast, and there isn't much that you can do to mitigate all of it, short of lining your entire room with 10mm thick lead, and standing outside during exposure.
As you know, I repair dental X-ray heads for a living. I receive scattered X-rays to my body every time I energize a head for testing. When I first got into this business about 13 years ago, I bought a lead-lined vest, which I wore every time I needed to test a head. But I soon stopped wearing it because it was heavy and cumbersome, and the slight amount of scattered X-rays that I receive during each exposure is negligable (I of course avoid the main beam by standing behind the energized head). Using a standard GM Geiger Counter, I was measuring various intensities of radiation all around my shop (which is the size of a 2-car garage). No radiation extends beyond the walls, and so my neighbors have nothing to worry about. The bottom line is, most scattered radiation that I receive is low-energy, which probably doesn't penetrate my skin. Also, most test exposures last less than one second, and I typically make 3 or 4 test exposures (<1 second each) to make sure that the repaired head is operating within manufacturer's specifications. I check KVp, mA, and MR, as well as off-axis radiation.
In general, where safety is concerned, a person needs to be reasonably protected from the threat without being overly protected to the point where he/she can no longer function. So, should you wear a lead lined vest? Sure, so long as it doesn't become a burden, and if the threat of damage to your health is significant. If you are not certain about the risk, then it's better to be safe than sorry.
Re: Grenadier's big thread of Röntgen related shenanigans
klugesmith, Tue Apr 12 2011, 07:59PM
I'll get your 200 mR pen dosimeter in the mail by tomorrow. Don't run it offscale on the first shot or two, or you'll be scrambling to get a charger for it. Normal digital-sensor exposures at my dentist's office register around 12 mR or 0.12 mGy.
Rich
klugesmith, Tue Apr 12 2011, 07:59PM
Grenadier wrote ...
It works :D
... And of course I couldn't call it a night without x-raying a few things.
Congratulations, Adam.It works :D
... And of course I couldn't call it a night without x-raying a few things.
I'll get your 200 mR pen dosimeter in the mail by tomorrow. Don't run it offscale on the first shot or two, or you'll be scrambling to get a charger for it. Normal digital-sensor exposures at my dentist's office register around 12 mR or 0.12 mGy.
Rich
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Wed Apr 13 2011, 05:47AM
That makes quite a bit of sense and I tried to reach 75kV today, but I got little done because mother nature rained on my radiation parade. I did notice something though; popping. I set up my camera on a 10sec timer to see what it was and it turns out the kilovoltmeter's resistor was sparking to the lead shield. How this was possible idunno, but I think it might be because something became a capacitor.
I was going to solve this with hot glue, but then the oil leaked all over and I swore something fierce. I've had it with leaking oil so I dumped it all out and then cleaned the outside of the PP as best I could with alcohol. I then put the lid on and hot glued the hell out of it (hot glue actually sticks to PP like cement). After that I punched a hole in the lid and used a pipette to squirt some degassed tranformer oil in there, then sealed up the hole with hot glue. So far it hasn't leaked, and if it doesn't leak then it ought to be good for a couple years.
Hopefully I have the beam centered right.
Adam Munich, Wed Apr 13 2011, 05:47AM
That makes quite a bit of sense and I tried to reach 75kV today, but I got little done because mother nature rained on my radiation parade. I did notice something though; popping. I set up my camera on a 10sec timer to see what it was and it turns out the kilovoltmeter's resistor was sparking to the lead shield.
How this was possible idunno, but I think it might be because something became a capacitor. I was going to solve this with hot glue, but then the oil leaked all over and I swore something fierce. I've had it with leaking oil so I dumped it all out and then cleaned the outside of the PP as best I could with alcohol. I then put the lid on and hot glued the hell out of it (hot glue actually sticks to PP like cement).
After that I punched a hole in the lid and used a pipette to squirt some degassed tranformer oil in there, then sealed up the hole with hot glue. So far it hasn't leaked, and if it doesn't leak then it ought to be good for a couple years. 
Hopefully I have the beam centered right.
Re: Grenadier's big thread of Röntgen related shenanigans
radhoo, Wed Apr 13 2011, 10:07AM
I'm starting to think oil created more problems for you than it solved.
Here are two opposite polarities Glassman multipliers working together for close to 140KV discharge (each multiplier is rated for 60KV max, I pushed them a little bit further):
If you look at the pictures you will see, there is no oil, only AIR in these multipliers, and there's no corona, not arcing, they were designed to work in air and they do a decent job.
Maybe this gives you some more ideas.
radhoo, Wed Apr 13 2011, 10:07AM
I'm starting to think oil created more problems for you than it solved.
Here are two opposite polarities Glassman multipliers working together for close to 140KV discharge (each multiplier is rated for 60KV max, I pushed them a little bit further):
If you look at the pictures you will see, there is no oil, only AIR in these multipliers, and there's no corona, not arcing, they were designed to work in air and they do a decent job.
Maybe this gives you some more ideas.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Wed Apr 13 2011, 10:41AM
Nah I solved the CW leaking, and I think I solved the tube leaking too now. The tube can't be run in air because it's so small (it'd flash right over in air), and the oil also convects away the anode heat..
Adam Munich, Wed Apr 13 2011, 10:41AM
Nah I solved the CW leaking, and I think I solved the tube leaking too now. The tube can't be run in air because it's so small (it'd flash right over in air), and the oil also convects away the anode heat..
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Wed Apr 20 2011, 03:17AM
Back to square one, minus $50. There is sparking inside the lead sheild and I have no way to solve it but to start over, this time putting everything under oil. Since I don't have enough lead sheet to make a new box I'm just going to make a very thick tube jacket, then put one layer of lead around the container and hope for the best. Of course I need to find a suitable oil-tight container now because I've freaking had it with oil leaking everywhere. I have not one pair of pants that hasn't been stained with oil...
I'm really losing my motivation,
Adam Munich, Wed Apr 20 2011, 03:17AM
Back to square one, minus $50. There is sparking inside the lead sheild and I have no way to solve it but to start over, this time putting everything under oil. Since I don't have enough lead sheet to make a new box I'm just going to make a very thick tube jacket, then put one layer of lead around the container and hope for the best. Of course I need to find a suitable oil-tight container now because I've freaking had it with oil leaking everywhere. I have not one pair of pants that hasn't been stained with oil...
I'm really losing my motivation,
Re: Grenadier's big thread of Röntgen related shenanigans
Xray, Wed Apr 20 2011, 05:11AM
Welcome to the world of X-ray equipment!
I wish I knew you (or rather, you wish you knew me) back in June of last year when I moved from Wisconsin to Minnesota. I got rid of a large box of lead shielding material (about 50 pounds of it!). Anyhow, there is some lead sheets in those heads I sent you. There should be enough to make another small box.
Xray, Wed Apr 20 2011, 05:11AM
Grenadier wrote ...
I have not one pair of pants that hasn't been stained with oil...
I have not one pair of pants that hasn't been stained with oil...
Welcome to the world of X-ray equipment!
I wish I knew you (or rather, you wish you knew me) back in June of last year when I moved from Wisconsin to Minnesota. I got rid of a large box of lead shielding material (about 50 pounds of it!). Anyhow, there is some lead sheets in those heads I sent you. There should be enough to make another small box.
Re: Grenadier's big thread of Röntgen related shenanigans
James, Wed Apr 20 2011, 05:39PM
Or maybe use one of the heads as a box? An x-ray head seems like the obvious thing to enclose a tube in :)
James, Wed Apr 20 2011, 05:39PM
Or maybe use one of the heads as a box? An x-ray head seems like the obvious thing to enclose a tube in :)
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Thu Apr 21 2011, 01:00AM
Using a head would be too easy! How could I say that I made anything if I just used a head?
Anyway... here is my "x-box"
Basically I put everything inside a PVC junction box, and it turned out awesome. I can't test it because I forgot to get a plug for that hole, and it's 37* and raining out. F*cking buffalo...
Nonetheless I used 6mm of lead for the tube jacket so very little external shielding should be needed. Funny how once you've spent months doing everything wrong, it takes only 5 hours to do it right.
Adam Munich, Thu Apr 21 2011, 01:00AM
Using a head would be too easy! How could I say that I made anything if I just used a head?
Anyway... here is my "x-box"
Basically I put everything inside a PVC junction box, and it turned out awesome. I can't test it because I forgot to get a plug for that hole, and it's 37* and raining out. F*cking buffalo...
Nonetheless I used 6mm of lead for the tube jacket so very little external shielding should be needed. Funny how once you've spent months doing everything wrong, it takes only 5 hours to do it right.
Re: Grenadier's big thread of Röntgen related shenanigans
James, Thu Apr 21 2011, 01:58AM
Well you didn't make the tube or the capacitor anyway, and there's that whole saying of no need to reinvent the wheel. That PVC junction box does look like a nice clean housing though.
James, Thu Apr 21 2011, 01:58AM
Well you didn't make the tube or the capacitor anyway, and there's that whole saying of no need to reinvent the wheel. That PVC junction box does look like a nice clean housing though.
Re: Grenadier's big thread of Röntgen related shenanigans
magnet18, Thu Apr 21 2011, 01:59AM
Experience, It's a wonderful thing.
Just gotta hang in there long enough to get it right.
magnet18, Thu Apr 21 2011, 01:59AM
Grenadier wrote ...
Funny how once you've spent months doing everything wrong, it takes only 5 hours to do it right.
Funny how once you've spent months doing everything wrong, it takes only 5 hours to do it right.
Experience, It's a wonderful thing.
Just gotta hang in there long enough to get it right.
Re: Grenadier's big thread of Röntgen related shenanigans
Xray, Thu Apr 21 2011, 02:36AM
Nice job, dude! It's clean and compact, and you even labeled the feed-through terminals! It looks much better than my first DIY "X-ray machine"!!!
Xray, Thu Apr 21 2011, 02:36AM
Grenadier wrote ...
Using a head would be too easy! How could I say that I made anything if I just used a head?
Anyway... here is my "x-box"
Using a head would be too easy! How could I say that I made anything if I just used a head?
Anyway... here is my "x-box"
Nice job, dude! It's clean and compact, and you even labeled the feed-through terminals! It looks much better than my first DIY "X-ray machine"!!!
Re: Grenadier's big thread of Röntgen related shenanigans
Wolfram, Thu Apr 21 2011, 03:24PM
Make sure you have some expansion volume for the oil, or you'll get an expensive lesson in thermal expansion when the oil gets hot. An air bubble in the oil is not a good idea, for obvious reasons. The usual solution is to use some sort of flexible membrane as a part of the outer casing, or a rubber bulb in the oil, either filled with air and sealed off, or vented to the outside of the casing.
Also, I second what James is saying. The actual x-ray head is only one sub-assembly of a complete x-ray machine, and whether you've used a complete manufactured x-ray head or put one together out of parts out of other x-ray machines makes little difference in the big picture. Doing it the way you have done can be a very valuable learning exercise though.
Wolfram, Thu Apr 21 2011, 03:24PM
Make sure you have some expansion volume for the oil, or you'll get an expensive lesson in thermal expansion when the oil gets hot. An air bubble in the oil is not a good idea, for obvious reasons. The usual solution is to use some sort of flexible membrane as a part of the outer casing, or a rubber bulb in the oil, either filled with air and sealed off, or vented to the outside of the casing.
Also, I second what James is saying. The actual x-ray head is only one sub-assembly of a complete x-ray machine, and whether you've used a complete manufactured x-ray head or put one together out of parts out of other x-ray machines makes little difference in the big picture. Doing it the way you have done can be a very valuable learning exercise though.
Re: Grenadier's big thread of Röntgen related shenanigans
Xray, Thu Apr 21 2011, 03:49PM
Yes, but make sure that any "rubber" or other flexible membrane that you use is compatible with oil. Natural rubber will deteriorate very quickly while in contact with oil. Most dental X-ray heads use "Buna-N" (aka, Nitrile) rubber, which can be in contact with oil for decades without deteriorating. Some heads utilize the actual housing for oil expansion/contraction which is made of a very thin steel sheetmetal, sort of like a can of Spam!
Xray, Thu Apr 21 2011, 03:49PM
Anders M. wrote ...
Make sure you have some expansion volume for the oil, or you'll get an expensive lesson in thermal expansion when the oil gets hot. An air bubble in the oil is not a good idea, for obvious reasons. The usual solution is to use some sort of flexible membrane as a part of the outer casing, or a rubber bulb in the oil, either filled with air and sealed off, or vented to the outside of the casing.
Make sure you have some expansion volume for the oil, or you'll get an expensive lesson in thermal expansion when the oil gets hot. An air bubble in the oil is not a good idea, for obvious reasons. The usual solution is to use some sort of flexible membrane as a part of the outer casing, or a rubber bulb in the oil, either filled with air and sealed off, or vented to the outside of the casing.
Yes, but make sure that any "rubber" or other flexible membrane that you use is compatible with oil. Natural rubber will deteriorate very quickly while in contact with oil. Most dental X-ray heads use "Buna-N" (aka, Nitrile) rubber, which can be in contact with oil for decades without deteriorating. Some heads utilize the actual housing for oil expansion/contraction which is made of a very thin steel sheetmetal, sort of like a can of Spam!
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Thu Apr 21 2011, 04:16PM
Yes I'm trying to think of a way to solve the expansion issue, as of right now there is just an air bubble in there.
Another issue, oil is seeping out. Not leaking out (no puddles of oil), but just a thin film is seeping out. I think I need some thicker oil, this transformer oil is thinner than water, pretty much as thin as acetone.
Hmm, maybe I could drill a hole in the rubber stopper, then superglue pice of a nitrile glove over the hole. I found these purple gloves in the basement and they aren't very stretchy, so they are likely nitrile.
Adam Munich, Thu Apr 21 2011, 04:16PM
Yes I'm trying to think of a way to solve the expansion issue, as of right now there is just an air bubble in there.
Another issue, oil is seeping out. Not leaking out (no puddles of oil), but just a thin film is seeping out. I think I need some thicker oil, this transformer oil is thinner than water, pretty much as thin as acetone.
Hmm, maybe I could drill a hole in the rubber stopper, then superglue pice of a nitrile glove over the hole. I found these purple gloves in the basement and they aren't very stretchy, so they are likely nitrile.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Thu Apr 21 2011, 05:28PM
Alright so here's what I came up with.
Basically I'm sticking a gove's finger in the hole and gluing it in place. It should work...
I needed a thicker oil so I found some husqvarna premium bar and chain oil. The stuff is as thick as maple syrup and by using a 9kV NST I figured out that its dielectric strength is about 10kV per mm, therefore it should be an excellent oil for this x-ray head.
*Let it be known that husqvarna premium bar and chain oil has a dielectric strength of 10kV per mm, and costs only 5 bux a quart*
Adam Munich, Thu Apr 21 2011, 05:28PM
Alright so here's what I came up with.
Basically I'm sticking a gove's finger in the hole and gluing it in place. It should work...
I needed a thicker oil so I found some husqvarna premium bar and chain oil. The stuff is as thick as maple syrup and by using a 9kV NST I figured out that its dielectric strength is about 10kV per mm, therefore it should be an excellent oil for this x-ray head.
*Let it be known that husqvarna premium bar and chain oil has a dielectric strength of 10kV per mm, and costs only 5 bux a quart*
Re: Grenadier's big thread of Röntgen related shenanigans
James, Thu Apr 21 2011, 05:38PM
Your plastic casing probably has enough flex to deal with expansion, although putting a sealed air filled rubber item inside is not a bad idea, maybe seal the end of a disposable plastic eye dropper or a small syringe?
Thick oil will wick out too if you have a leak. Did you seal the feedthroughs with silicone or epoxy on the inside?
James, Thu Apr 21 2011, 05:38PM
Your plastic casing probably has enough flex to deal with expansion, although putting a sealed air filled rubber item inside is not a bad idea, maybe seal the end of a disposable plastic eye dropper or a small syringe?
Thick oil will wick out too if you have a leak. Did you seal the feedthroughs with silicone or epoxy on the inside?
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Thu Apr 21 2011, 06:20PM
No it's sealed with a foam gasket and the feedthroughs are sealed with rubber washers. So far, no leaks!
As for the expansion thing, I just cut off a finger and stuck it in the hole. It works and it doesn't leak, even without glue. I like this oil a lot.
Adam Munich, Thu Apr 21 2011, 06:20PM
No it's sealed with a foam gasket and the feedthroughs are sealed with rubber washers. So far, no leaks!
As for the expansion thing, I just cut off a finger and stuck it in the hole. It works and it doesn't leak, even without glue. I like this oil a lot.
Re: Grenadier's big thread of Röntgen related shenanigans
Proud Mary, Thu Apr 21 2011, 06:35PM
What is the maximum pd between Gnd and HV across the surface of the case?
Proud Mary, Thu Apr 21 2011, 06:35PM
What is the maximum pd between Gnd and HV across the surface of the case?
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Thu Apr 21 2011, 07:10PM
19kV, I made sure to space them apart enough. If not I can always glue a little piece of plastic in between them.
Adam Munich, Thu Apr 21 2011, 07:10PM
19kV, I made sure to space them apart enough. If not I can always glue a little piece of plastic in between them.
Re: Grenadier's big thread of Röntgen related shenanigans
Proud Mary, Thu Apr 21 2011, 08:40PM
Perhaps you might want to do that before powering up for the first time. Once surface tracking has started, you might not notice it until the course of the tracks is too well established to get rid of.
Ionic surface contamination - perspiration, for example - helps set the scene for tracking breakdown.
Dielectric surface discharges are complex phenomena, so you mustn't think of your GND and HV terminals as though they were simply separated by air.
Powering up in complete darkness, and then looking for the presence of streamers once your eyes have adjusted, may help you identify spawning problems.
Proud Mary, Thu Apr 21 2011, 08:40PM
Grenadier wrote ...
19kV, I made sure to space them apart enough. If not I can always glue a little piece of plastic in between them.
19kV, I made sure to space them apart enough. If not I can always glue a little piece of plastic in between them.
Perhaps you might want to do that before powering up for the first time. Once surface tracking has started, you might not notice it until the course of the tracks is too well established to get rid of.
Ionic surface contamination - perspiration, for example - helps set the scene for tracking breakdown.
Dielectric surface discharges are complex phenomena, so you mustn't think of your GND and HV terminals as though they were simply separated by air.
Powering up in complete darkness, and then looking for the presence of streamers once your eyes have adjusted, may help you identify spawning problems.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Thu Apr 21 2011, 09:26PM
Hmm, I'll probably do that then, although the distance between the 2 terminals is about the same as the distance on the flyback's container and nothing seems to have gone wrong there, even tough it's been powered up multiple times.
I suppose nothing can go wrong by putting plastic there though, now to find a shard of plastic...
Adam Munich, Thu Apr 21 2011, 09:26PM
Hmm, I'll probably do that then, although the distance between the 2 terminals is about the same as the distance on the flyback's container and nothing seems to have gone wrong there, even tough it's been powered up multiple times.
I suppose nothing can go wrong by putting plastic there though, now to find a shard of plastic...
Re: Grenadier's big thread of Röntgen related shenanigans
James, Thu Apr 21 2011, 09:40PM
That sounds a little extreme :)
James, Thu Apr 21 2011, 09:40PM
Grenadier wrote ...
As for the expansion thing, I just cut off a finger and stuck it in the hole. It works and it doesn't leak, even without glue.
As for the expansion thing, I just cut off a finger and stuck it in the hole. It works and it doesn't leak, even without glue.
That sounds a little extreme :)
Re: Grenadier's big thread of Röntgen related shenanigans
magnet18, Fri Apr 22 2011, 02:07AM
I had surface tracking occur on a flyback before from pin to pin... that flyback is no more.
Theres not much you can do about it once it starts, so make sure it doesn't.
magnet18, Fri Apr 22 2011, 02:07AM
I had surface tracking occur on a flyback before from pin to pin... that flyback is no more.
Theres not much you can do about it once it starts, so make sure it doesn't.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Fri Apr 22 2011, 05:52AM
I am now in possession of the most awesome kilovoltmeter ever.
Wait for it... Boom!
Adam Munich, Fri Apr 22 2011, 05:52AM
I am now in possession of the most awesome kilovoltmeter ever.
Wait for it... Boom!
Re: Grenadier's big thread of Röntgen related shenanigans
magnet18, Fri Apr 22 2011, 10:25AM
I want one...
magnet18, Fri Apr 22 2011, 10:25AM
Grenadier wrote ...
I am now in possession of the most awesome kilovoltmeter ever.
Wait for it... Boom!
I am now in possession of the most awesome kilovoltmeter ever.
Wait for it... Boom!
I want one...
Re: Grenadier's big thread of Röntgen related shenanigans
Xray, Fri Apr 22 2011, 02:47PM
That meter by itself can't measure hv, right? I suspect that it is only part of a complete meter assembly that includes a hv resistor dividor.
Xray, Fri Apr 22 2011, 02:47PM
Grenadier wrote ...
I am now in possession of the most awesome kilovoltmeter ever.
Wait for it... Boom!
I am now in possession of the most awesome kilovoltmeter ever.
Wait for it... Boom!
That meter by itself can't measure hv, right? I suspect that it is only part of a complete meter assembly that includes a hv resistor dividor.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Fri Apr 22 2011, 03:19PM
Yes the divider is inside the tubehead, it's a 1.8G resistor string. (4x 450M resistors)
Adam Munich, Fri Apr 22 2011, 03:19PM
Yes the divider is inside the tubehead, it's a 1.8G resistor string. (4x 450M resistors)
Re: Grenadier's big thread of Röntgen related shenanigans
James, Fri Apr 22 2011, 05:06PM
If you catch it quick enough and cut the power, you can usually scrape off the carbon and apply some silicone to keep it from arcing.
James, Fri Apr 22 2011, 05:06PM
magnet18 wrote ...
I had surface tracking occur on a flyback before from pin to pin... that flyback is no more.
Theres not much you can do about it once it starts, so make sure it doesn't.
I had surface tracking occur on a flyback before from pin to pin... that flyback is no more.
Theres not much you can do about it once it starts, so make sure it doesn't.
If you catch it quick enough and cut the power, you can usually scrape off the carbon and apply some silicone to keep it from arcing.
Re: Grenadier's big thread of Röntgen related shenanigans
magnet18, Fri Apr 22 2011, 08:16PM
My bad, meant to say once it's established.
on a similar note... superglue is conductive... and it burns bright yellow.
[EDIT]
@ grenadier, where does the backlight (I'm assuming LED's) get it's power?
magnet18, Fri Apr 22 2011, 08:16PM
James wrote ...
If you catch it quick enough and cut the power, you can usually scrape off the carbon and apply some silicone to keep it from arcing.
magnet18 wrote ...
I had surface tracking occur on a flyback before from pin to pin... that flyback is no more.
Theres not much you can do about it once it starts, so make sure it doesn't.
I had surface tracking occur on a flyback before from pin to pin... that flyback is no more.
Theres not much you can do about it once it starts, so make sure it doesn't.
If you catch it quick enough and cut the power, you can usually scrape off the carbon and apply some silicone to keep it from arcing.
My bad, meant to say once it's established.
on a similar note... superglue is conductive... and it burns bright yellow.
[EDIT]
@ grenadier, where does the backlight (I'm assuming LED's) get it's power?
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Fri May 27 2011, 03:11AM
Alright then here is what I have.
A working multiplexed nixie display, a new box with a CNC'd cover, and most of the circuitry, aside from the battery section done.
Now I have come to a crossroad, should I glue a second box to it like I did before, or should I keep the actual x-ray head seperate and connect it via a cable? I could fasion a cable using octal base tube sockets and some hose. Keeping the head seperate means that positioning it will be easier, however that also means that some potentially high voltage wires will need to go back to the meters.
If the meters are working OK the wires will be at low voltages, <10V, however if a meter goes open circuit then those wires are no longer pulled down to ground and will get quite hot. Example, the mA meter is in series with the tube and ground. If it goes open circuit then one side is +HV and the other is ground. Maybe some MOVs could protect things...
Adam Munich, Fri May 27 2011, 03:11AM
Alright then here is what I have.
A working multiplexed nixie display, a new box with a CNC'd cover, and most of the circuitry, aside from the battery section done.
Now I have come to a crossroad, should I glue a second box to it like I did before, or should I keep the actual x-ray head seperate and connect it via a cable? I could fasion a cable using octal base tube sockets and some hose. Keeping the head seperate means that positioning it will be easier, however that also means that some potentially high voltage wires will need to go back to the meters.
If the meters are working OK the wires will be at low voltages, <10V, however if a meter goes open circuit then those wires are no longer pulled down to ground and will get quite hot. Example, the mA meter is in series with the tube and ground. If it goes open circuit then one side is +HV and the other is ground. Maybe some MOVs could protect things...
Re: Grenadier's big thread of Röntgen related shenanigans
klugesmith, Fri May 27 2011, 03:49AM
Nice work.
A similar approach can protect your kV-measurement circuit. In that case, if full-scale meter current is in the 10-to-20 uA range, the FS meter voltage may be high enough for a regular protective shunt diode to conduct significantly.
klugesmith, Fri May 27 2011, 03:49AM
Nice work.
Grenadier wrote ...
Example, the mA meter is in series with the tube and ground. If it goes open circuit then one side is +HV and the other is ground. Maybe some MOVs could protect things...
For that example, in the likely case that mA meter's full scale voltage is not more than 200 mV: Shunt the mA-meter circuit at the HV end with hefty diodes in both directions, and a capacitor. Then at the control end, even if meter is disconnected there's no HV. The shunt should be able to withstand the maximum HV current under fault conditions, such as an unexpected arc in parallel with your Coolidge tube.Example, the mA meter is in series with the tube and ground. If it goes open circuit then one side is +HV and the other is ground. Maybe some MOVs could protect things...
A similar approach can protect your kV-measurement circuit. In that case, if full-scale meter current is in the 10-to-20 uA range, the FS meter voltage may be high enough for a regular protective shunt diode to conduct significantly.
Re: Grenadier's big thread of Röntgen related shenanigans
Xray, Fri May 27 2011, 02:42PM
If any point along the mA circuit should open, then the open circuit will arc like a spark gap when the hv is energized. In fact, some older X-ray heads have a small spark gap mounted right at the mA terminal on the head to handle that particular situation. Newer models use a commercially available gas-filled voltage snubber (I'm not sure if that's really what they are called). It's bascially a neon bulb. And that's what you can use in your X-ray head. A typical neon bulb will fire at around 85 volts, and it should be able to handle the current from your CW multiplier for some time period.
Nice job, Adam!
Xray, Fri May 27 2011, 02:42PM
Grenadier wrote ...
If the meters are working OK the wires will be at low voltages, <10V, however if a meter goes open circuit then those wires are no longer pulled down to ground and will get quite hot. Example, the mA meter is in series with the tube and ground. If it goes open circuit then one side is +HV and the other is ground. Maybe some MOVs could protect things...
If the meters are working OK the wires will be at low voltages, <10V, however if a meter goes open circuit then those wires are no longer pulled down to ground and will get quite hot. Example, the mA meter is in series with the tube and ground. If it goes open circuit then one side is +HV and the other is ground. Maybe some MOVs could protect things...
If any point along the mA circuit should open, then the open circuit will arc like a spark gap when the hv is energized. In fact, some older X-ray heads have a small spark gap mounted right at the mA terminal on the head to handle that particular situation. Newer models use a commercially available gas-filled voltage snubber (I'm not sure if that's really what they are called). It's bascially a neon bulb. And that's what you can use in your X-ray head. A typical neon bulb will fire at around 85 volts, and it should be able to handle the current from your CW multiplier for some time period.
Nice job, Adam!
Re: Grenadier's big thread of Röntgen related shenanigans
klugesmith, Fri May 27 2011, 03:47PM
The name is gas tube surge arrestor. e.g.
The ones pictured can probably handle short pulses of over 1000 amps.
I can send you a few that look like three-terminal neon lamps.
klugesmith, Fri May 27 2011, 03:47PM
Xray wrote ...
... Newer models use a commercially available gas-filled voltage snubber (I'm not sure if that's really what they are called). It's bascially a neon bulb. And that's what you can use in your X-ray head.
Excellent suggestion - a single, inexpensive, very robust part. ... Newer models use a commercially available gas-filled voltage snubber (I'm not sure if that's really what they are called). It's bascially a neon bulb. And that's what you can use in your X-ray head.
The name is gas tube surge arrestor. e.g.
The ones pictured can probably handle short pulses of over 1000 amps.
I can send you a few that look like three-terminal neon lamps.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Sat May 28 2011, 04:05PM
That is a clever idea using the neon lamps as protection, sure have enough of those. I've got a couple 1kV gas tube surge arrestors, I've always wondered whether or not a mark generator could be made 100% reliable by using those things in series instead of spark gaps.
I found this nice ceramic octal base that I could use for the control box's connection, but as for the head I'll have to use a plastic one as I have no more ceramic ones. I just need to find a pair of octal bases or tubes, all my tubes are nice GE and RCA ones (which I'd prefer to not destroy). I'll need to stain my box and try not destroy it...
Anyone else notice that my posts sound more intelligent during the day?
Adam Munich, Sat May 28 2011, 04:05PM
That is a clever idea using the neon lamps as protection, sure have enough of those. I've got a couple 1kV gas tube surge arrestors, I've always wondered whether or not a mark generator could be made 100% reliable by using those things in series instead of spark gaps.
I found this nice ceramic octal base that I could use for the control box's connection, but as for the head I'll have to use a plastic one as I have no more ceramic ones. I just need to find a pair of octal bases or tubes, all my tubes are nice GE and RCA ones (which I'd prefer to not destroy). I'll need to stain my box and try not destroy it...
Anyone else notice that my posts sound more intelligent during the day?
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Mon May 30 2011, 03:15PM
Despite my best efforts, the stain looks like crap. Apparently this is just bad wood, grown and harvested in a hurry. My only option now is flat black rustoleum and some lacquer over that to make it nice and shiny.
Of course I could always do a 2 color design... if that is the case what colors and what design? Baby blue and white maybe?
Ideas plz!
Adam Munich, Mon May 30 2011, 03:15PM
Despite my best efforts, the stain looks like crap. Apparently this is just bad wood, grown and harvested in a hurry. My only option now is flat black rustoleum and some lacquer over that to make it nice and shiny.
Of course I could always do a 2 color design... if that is the case what colors and what design? Baby blue and white maybe?
Ideas plz!
Re: Grenadier's big thread of Röntgen related shenanigans
Xray, Mon May 30 2011, 05:00PM
Back in the "olden days" (before MY time!) electronic equipment control panels were painted with a textured paint called "crincle", and the prefered color was black. Then in the 1950's and 1960's, they were using a textured paint called "hammertone". and the prefered color was gray. Either of those two paint styles should hide most of the grain and defects in the wood. And that type of paint will give your project a vintage look. Both of those textures are still available from paint manufacturers.
Xray, Mon May 30 2011, 05:00PM
Grenadier wrote ...
Despite my best efforts, the stain looks like crap. Apparently this is just bad wood, grown and harvested in a hurry. My only option now is flat black rustoleum and some lacquer over that to make it nice and shiny.
Of course I could always do a 2 color design... if that is the case what colors and what design? Baby blue and white maybe?
Ideas plz!
Despite my best efforts, the stain looks like crap. Apparently this is just bad wood, grown and harvested in a hurry. My only option now is flat black rustoleum and some lacquer over that to make it nice and shiny.
Of course I could always do a 2 color design... if that is the case what colors and what design? Baby blue and white maybe?
Ideas plz!
Back in the "olden days" (before MY time!) electronic equipment control panels were painted with a textured paint called "crincle", and the prefered color was black. Then in the 1950's and 1960's, they were using a textured paint called "hammertone". and the prefered color was gray. Either of those two paint styles should hide most of the grain and defects in the wood. And that type of paint will give your project a vintage look. Both of those textures are still available from paint manufacturers.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Mon May 30 2011, 05:22PM
Problem is you need to bake those paints to get the effect, and putting pine in a 200* oven isn't exactly the best thing to do. (sap... everywhere!)
Adam Munich, Mon May 30 2011, 05:22PM
Problem is you need to bake those paints to get the effect, and putting pine in a 200* oven isn't exactly the best thing to do. (sap... everywhere!)
Re: Grenadier's big thread of Röntgen related shenanigans
Xray, Mon May 30 2011, 05:49PM
Actually, no you don't need to bake the paint. It comes right out of the can that way. Go ahead and Google "hammertone paint". There are also many other types textured paints available at most hardware stores, if that's the direction you want to go.
Xray, Mon May 30 2011, 05:49PM
Grenadier wrote ...
Problem is you need to bake those paints to get the effect, and putting pine in a 200* oven isn't exactly the best thing to do. (sap... everywhere!)
Problem is you need to bake those paints to get the effect, and putting pine in a 200* oven isn't exactly the best thing to do. (sap... everywhere!)
Actually, no you don't need to bake the paint. It comes right out of the can that way. Go ahead and Google "hammertone paint". There are also many other types textured paints available at most hardware stores, if that's the direction you want to go.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Mon May 30 2011, 08:03PM
Got back from home depot, every hammer on or wrinkle paint they had needed a bake.
I'm just going to do a 2 color thing and then clearcoat, but before that I'm going to layer the primer on (sand between coats) until the wood grain can't be seen anymore.
Adam Munich, Mon May 30 2011, 08:03PM
Got back from home depot, every hammer on or wrinkle paint they had needed a bake.
I'm just going to do a 2 color thing and then clearcoat, but before that I'm going to layer the primer on (sand between coats) until the wood grain can't be seen anymore.
Re: Grenadier's big thread of Röntgen related shenanigans
Xray, Mon May 30 2011, 08:27PM
Here are two types of "hammered" paint made by Krylon: Neither of them requires elevated temperature to cure.
Xray, Mon May 30 2011, 08:27PM
Grenadier wrote ...
Got back from home depot, every hammer on or wrinkle paint they had needed a bake.
I'm just going to do a 2 color thing and then clearcoat, but before that I'm going to layer the primer on (sand between coats) until the wood grain can't be seen anymore.
Got back from home depot, every hammer on or wrinkle paint they had needed a bake.
I'm just going to do a 2 color thing and then clearcoat, but before that I'm going to layer the primer on (sand between coats) until the wood grain can't be seen anymore.
Here are two types of "hammered" paint made by Krylon:
Neither of them requires elevated temperature to cure.Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Tue May 31 2011, 04:32AM
I'll look for the hammered paint then because the wood grain still shows through.
Maybe I can use the hammered as a primer and then do the bi color thing over it, then lacquer.
My concern with the hammer paint is well, it's textured and putting labels on the machine is kind of hard when things are all bumpy.
Adam Munich, Tue May 31 2011, 04:32AM
I'll look for the hammered paint then because the wood grain still shows through.
Maybe I can use the hammered as a primer and then do the bi color thing over it, then lacquer.
My concern with the hammer paint is well, it's textured and putting labels on the machine is kind of hard when things are all bumpy.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Wed Jun 01 2011, 04:34AM
I done and found the hammered paint.
Accidentally put too many coats on the control panel face of the box so it's less bumpy than the rest of the box, but not that noticeable. To hell with bi-color, this looks awesome as it is.
So far no cat hairs on the paint, and no loss of consciousness from all the xylene fumes in the basement. Thanks for the tip x-ray.
Adam Munich, Wed Jun 01 2011, 04:34AM
I done and found the hammered paint.
Accidentally put too many coats on the control panel face of the box so it's less bumpy than the rest of the box, but not that noticeable. To hell with bi-color, this looks awesome as it is.
So far no cat hairs on the paint, and no loss of consciousness from all the xylene fumes in the basement. Thanks for the tip x-ray.
Re: Grenadier's big thread of Röntgen related shenanigans
Xray, Wed Jun 01 2011, 02:40PM
Your panel looks great! I used hammered paint on a panel that I made for my vacuum gauge about 10 years ago, and it's holding up very well. It's even resistant to oil being splashed on it!
Xray, Wed Jun 01 2011, 02:40PM
Your panel looks great! I used hammered paint on a panel that I made for my vacuum gauge about 10 years ago, and it's holding up very well. It's even resistant to oil being splashed on it!
Re: Grenadier's big thread of Röntgen related shenanigans
magnet18, Wed Jun 01 2011, 08:03PM
That thing looks industrially awesome!
For the cable connecting the two boxes, I would wrap the wires in electrical tape and put them in that plastic conduit stuff they sell. Partially because it looks cool and should fit in well with that box, and partially to protect any body parts next to the wires on the off chance that they go HV.
Just my two cents.
magnet18, Wed Jun 01 2011, 08:03PM
That thing looks industrially awesome!
For the cable connecting the two boxes, I would wrap the wires in electrical tape and put them in that plastic conduit stuff they sell. Partially because it looks cool and should fit in well with that box, and partially to protect any body parts next to the wires on the off chance that they go HV.
Just my two cents.
Re: Grenadier's big thread of Röntgen related shenanigans
Proud Mary, Wed Jun 01 2011, 08:43PM
My, that has turned out well, Adam.
I use Hammerite - the UK equivalent - on everything I make. and it does very well in concealing small scratches and blemishes.
In wintertime, I set the touch-dry panels or chassis on top of the radiators for a couple of days, to really bake the coat on.
Proud Mary, Wed Jun 01 2011, 08:43PM
My, that has turned out well, Adam.
I use Hammerite - the UK equivalent - on everything I make. and it does very well in concealing small scratches and blemishes.
In wintertime, I set the touch-dry panels or chassis on top of the radiators for a couple of days, to really bake the coat on.
Re: Grenadier's big thread of Röntgen related shenanigans
magnet18, Wed Jun 01 2011, 10:05PM
What's the etch a sketch for?
Bored while the paint dries?
magnet18, Wed Jun 01 2011, 10:05PM
Grenadier wrote ...
I done and found the hammered paint.
Accidentally put too many coats on the control panel face of the box so it's less bumpy than the rest of the box, but not that noticeable. To hell with bi-color, this looks awesome as it is.
I done and found the hammered paint.
Accidentally put too many coats on the control panel face of the box so it's less bumpy than the rest of the box, but not that noticeable. To hell with bi-color, this looks awesome as it is.
What's the etch a sketch for?
Bored while the paint dries?
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Wed Jun 01 2011, 10:13PM
Yeah pretty much.
The paint doesn't go a very long way, I need to get another can to put another coat on the other half of the box. The paint is dry on both pieces, however it is still soft and probably will take a few days to harden.
Turns out that the 'paint' is lacquer with some dye and powdered mica mixed in. Therefore I won't need the finishing coat of lacquer, so good news there.
I now need to pick a box for the head part of the machine, hopefully it will be smaller than this one but I might have to get the same size box if I can't fit the flyback inside the smaller one.
Been writing the code to control the machine, so far it looks like it will work. Has a safety countdown and stuff. Still have to find some octal bases, and as for making the cable ideally I'd like to find cloth covered tubing, but that might be a long shot.
Adam Munich, Wed Jun 01 2011, 10:13PM
Yeah pretty much.
The paint doesn't go a very long way, I need to get another can to put another coat on the other half of the box. The paint is dry on both pieces, however it is still soft and probably will take a few days to harden.
Turns out that the 'paint' is lacquer with some dye and powdered mica mixed in. Therefore I won't need the finishing coat of lacquer, so good news there.
I now need to pick a box for the head part of the machine, hopefully it will be smaller than this one but I might have to get the same size box if I can't fit the flyback inside the smaller one.
Been writing the code to control the machine, so far it looks like it will work. Has a safety countdown and stuff. Still have to find some octal bases, and as for making the cable ideally I'd like to find cloth covered tubing, but that might be a long shot.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Thu Jun 02 2011, 02:38AM
Of course the can never told me to not put another coat on after the paint dried... everything flaked off the box (not the lid, which I did not paint again)
So... after a bunch of acetone I stripped the paint off the box and put some new stuff on. Oh well, sht happens.
Adam Munich, Thu Jun 02 2011, 02:38AM
Of course the can never told me to not put another coat on after the paint dried... everything flaked off the box (not the lid, which I did not paint again)
So... after a bunch of acetone I stripped the paint off the box and put some new stuff on. Oh well, sht happens.
Re: Grenadier's big thread of Röntgen related shenanigans
magnet18, Thu Jun 02 2011, 03:17AM
Flyback? I thought it was powered by an xray transformer?
magnet18, Thu Jun 02 2011, 03:17AM
Flyback? I thought it was powered by an xray transformer?
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Thu Jun 02 2011, 03:20AM
Nope, it's a battery powered machine.
LiPo Batts > Royer Oscillator > Flyback Transformer > Cockroft walton > Coolidge tube
That reminds me, I need to go buy some LiPos.
Adam Munich, Thu Jun 02 2011, 03:20AM
Nope, it's a battery powered machine.
LiPo Batts > Royer Oscillator > Flyback Transformer > Cockroft walton > Coolidge tube
That reminds me, I need to go buy some LiPos.
Re: Grenadier's big thread of Röntgen related shenanigans
magnet18, Thu Jun 02 2011, 11:08AM
schmancy, I'm impressed
magnet18, Thu Jun 02 2011, 11:08AM
schmancy, I'm impressed
Re: Grenadier's big thread of Röntgen related shenanigans
Xray, Thu Jun 02 2011, 04:23PM
When painting over a dried layer of paint, it's recommended to lightly sand the surface so that it's no longer shiney. The new coat will adhere much better.
Xray, Thu Jun 02 2011, 04:23PM
Grenadier wrote ...
Of course the can never told me to not put another coat on after the paint dried... everything flaked off the box (not the lid, which I did not paint again)
So... after a bunch of acetone I stripped the paint off the box and put some new stuff on. Oh well, sht happens.
Of course the can never told me to not put another coat on after the paint dried... everything flaked off the box (not the lid, which I did not paint again)
So... after a bunch of acetone I stripped the paint off the box and put some new stuff on. Oh well, sht happens.
When painting over a dried layer of paint, it's recommended to lightly sand the surface so that it's no longer shiney. The new coat will adhere much better.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Thu Jun 02 2011, 04:25PM
No, the old coat peeled off. :-/
That aside, the new coat is on and in a few days it should be hard to the point in where I can handle it without leaving marks.
Adam Munich, Thu Jun 02 2011, 04:25PM
No, the old coat peeled off. :-/
That aside, the new coat is on and in a few days it should be hard to the point in where I can handle it without leaving marks.
Re: Grenadier's big thread of Röntgen related shenanigans
magnet18, Thu Jun 02 2011, 07:49PM
Just an idea for when it works, xray a nixie.
Might look cool.
magnet18, Thu Jun 02 2011, 07:49PM
Just an idea for when it works, xray a nixie.
Might look cool.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Fri Jun 03 2011, 01:17AM
Because the head is separate from the control box, I'll be able to x-ray the x-ray machine itself!
Waiting for the paint to harden sucks...
Adam Munich, Fri Jun 03 2011, 01:17AM
Because the head is separate from the control box, I'll be able to x-ray the x-ray machine itself!
Waiting for the paint to harden sucks...
Re: Grenadier's big thread of Röntgen related shenanigans
magnet18, Fri Jun 03 2011, 03:15AM
That's actually what gave me the idea to xray the nixies
I wasn't sure if the xrays would ruin the arduino or anything.
Did you find a box for the head yet?
magnet18, Fri Jun 03 2011, 03:15AM
That's actually what gave me the idea to xray the nixies
I wasn't sure if the xrays would ruin the arduino or anything.
Did you find a box for the head yet?
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Sun Jun 05 2011, 07:00PM
This paint is still soft, and leaves marks when handled. I hope it will dry before I grow old and die...
Adam Munich, Sun Jun 05 2011, 07:00PM
This paint is still soft, and leaves marks when handled. I hope it will dry before I grow old and die...
Re: Grenadier's big thread of Röntgen related shenanigans
magnet18, Mon Jun 06 2011, 01:06AM
Have you tried heating it?
magnet18, Mon Jun 06 2011, 01:06AM
Have you tried heating it?
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Tue Jun 07 2011, 02:37AM
I got impatient and put the box together. The paint is curing, albiet very slowly. I'll just avoid touching it until it's cured.
Turned out pretty well, even if it isn't perfect. Now I just need to make it work because right now it's just a fancy box with knobs on it.
Time to buy some lipos. I settled on a 4000mAh 14.4V one and a 3000mAh 22.2V one. They'll go in series and the 14V one will also supply power to the control circuitry and tube heater. (tis the reason why it is larger).
Adam Munich, Tue Jun 07 2011, 02:37AM
I got impatient and put the box together. The paint is curing, albiet very slowly. I'll just avoid touching it until it's cured.
Turned out pretty well, even if it isn't perfect. Now I just need to make it work because right now it's just a fancy box with knobs on it.
Time to buy some lipos. I settled on a 4000mAh 14.4V one and a 3000mAh 22.2V one. They'll go in series and the 14V one will also supply power to the control circuitry and tube heater. (tis the reason why it is larger).
Re: Grenadier's big thread of Röntgen related shenanigans
magnet18, Tue Jun 07 2011, 03:06AM
I'm officially jealous.
I want one.
magnet18, Tue Jun 07 2011, 03:06AM
I'm officially jealous.
I want one.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Fri Jun 10 2011, 04:55AM
Started putting in some circuitry, but really can't do much more of that until the batteries get here.
Time to start working on the tube head then.
Adam Munich, Fri Jun 10 2011, 04:55AM
Started putting in some circuitry, but really can't do much more of that until the batteries get here.
Time to start working on the tube head then.
Re: Grenadier's big thread of Röntgen related shenanigans
Xray, Fri Jun 10 2011, 06:04AM
Wow! Your panel looks great! You can also dress it up with some rub-on letter transfers so that the operator knows what each button, knob, and light is for.
Xray, Fri Jun 10 2011, 06:04AM
Wow! Your panel looks great! You can also dress it up with some rub-on letter transfers so that the operator knows what each button, knob, and light is for.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Wed Jun 15 2011, 02:56AM
What I did:
*Got the nixies working
*Got the microcontroller working
*Got the batteries in the mail
*Put battery in backwards
*Killed everything.
*Fixed everything, save for the atmega168. Now I need to wait a week for more in the mail :-/.
Adam Munich, Wed Jun 15 2011, 02:56AM
What I did:
*Got the nixies working
*Got the microcontroller working
*Got the batteries in the mail
*Put battery in backwards
*Killed everything.
*Fixed everything, save for the atmega168. Now I need to wait a week for more in the mail :-/.
Re: Grenadier's big thread of Röntgen related shenanigans
magnet18, Wed Jun 15 2011, 06:09AM
I put 10 transistors in backwards for my nixie clock.
Seriously spent 4 days working on it and couldn't figure out why all the digits were lighting up, the collector&base waveforms made no sense whatsoever.
Then I checked the datasheet, smashed my head to my desk, and spend 20 minuets ripping it out and a good 5 hours doing it again.
My point being, sh*t happens.
magnet18, Wed Jun 15 2011, 06:09AM
I put 10 transistors in backwards for my nixie clock.
Seriously spent 4 days working on it and couldn't figure out why all the digits were lighting up, the collector&base waveforms made no sense whatsoever.
Then I checked the datasheet, smashed my head to my desk, and spend 20 minuets ripping it out and a good 5 hours doing it again.
My point being, sh*t happens.
Re: Grenadier's big thread of Röntgen related shenanigans
Xray, Wed Jun 15 2011, 03:21PM
If I had a dollar for every time I've done something like that, I'd be very rich! I recall a time when I soldered a 50-pin circular connector on a cable. I was very careful to make sure that the wire colors matched the correct pin numbers, and I even placed heat-shrink tubing on each and every soldered connection. After I got done admiring my work, I realized that I had forgotten to install the connector shell before soldering the connector pins! It was the type of shell that isn't split, and so you had to slide it onto the cable before attaching the connector. The other end of the cable had another 50-pin connector on it, so I couldn't simply slide the shell over the other end. Needless to say, I was quite upset with myself.
Experienced carpenters adhere to an old motto: "Measure twice, cut once." Those of us in the electronics industry should adopt a similar motto. Something like: "Check the data sheet twice, solder once."
Xray, Wed Jun 15 2011, 03:21PM
magnet18 wrote ...
I put 10 transistors in backwards for my nixie clock.
Seriously spent 4 days working on it and couldn't figure out why all the digits were lighting up, the collector&base waveforms made no sense whatsoever.
Then I checked the datasheet, smashed my head to my desk, and spend 20 minuets ripping it out and a good 5 hours doing it again.
My point being, sh*t happens.
I put 10 transistors in backwards for my nixie clock.
Seriously spent 4 days working on it and couldn't figure out why all the digits were lighting up, the collector&base waveforms made no sense whatsoever.
Then I checked the datasheet, smashed my head to my desk, and spend 20 minuets ripping it out and a good 5 hours doing it again.
My point being, sh*t happens.
If I had a dollar for every time I've done something like that, I'd be very rich! I recall a time when I soldered a 50-pin circular connector on a cable. I was very careful to make sure that the wire colors matched the correct pin numbers, and I even placed heat-shrink tubing on each and every soldered connection. After I got done admiring my work, I realized that I had forgotten to install the connector shell before soldering the connector pins! It was the type of shell that isn't split, and so you had to slide it onto the cable before attaching the connector. The other end of the cable had another 50-pin connector on it, so I couldn't simply slide the shell over the other end. Needless to say, I was quite upset with myself.
Experienced carpenters adhere to an old motto: "Measure twice, cut once." Those of us in the electronics industry should adopt a similar motto. Something like: "Check the data sheet twice, solder once."
Re: Grenadier's big thread of Röntgen related shenanigans
Ash Small, Wed Jun 15 2011, 03:45PM
I built an electro-polishing setup in '98. Got everything sorted, mixed the chemicals, heated them to working temp., connected the rectifier to the supply, connected the workpiece (a stainless steel component), used another piece of stainless sheet for the cathode, switched on.....waited........turned it off, checked the workpiece and it looked worse than when I started.
Tried again......same thing......and again.....I was really disillusioned by now.....things normally work first time for me.....
I stripped it all down, waited for the electrolyte to cool....and removed the cathode.....surprise, surprise....I could see my face in it......somehow I'd managed to connect the anode and cathode up the wrong way round....
Ash Small, Wed Jun 15 2011, 03:45PM
I built an electro-polishing setup in '98. Got everything sorted, mixed the chemicals, heated them to working temp., connected the rectifier to the supply, connected the workpiece (a stainless steel component), used another piece of stainless sheet for the cathode, switched on.....waited........turned it off, checked the workpiece and it looked worse than when I started.
Tried again......same thing......and again.....I was really disillusioned by now.....things normally work first time for me.....
I stripped it all down, waited for the electrolyte to cool....and removed the cathode.....surprise, surprise....I could see my face in it......somehow I'd managed to connect the anode and cathode up the wrong way round....
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Thu Jun 16 2011, 03:15AM
Well to pass time I started working on the tube head today. Once again the paint is very inconsistent, but this time it actually dried. I used regular rustoleum hammered rather than "universal" rustoleum hammered. Each face of the box has it's own special thing going on, with the top being lumpy, the sides being bumpy and the back being wrinkled/crackled. I give up on making things consistent though, it's just not happening.
[no pic taken...]
For the tube heater I used an adjustable 3A switch mode power supply IC. All you need to do is use one resistor to set the frequency and a resistive divider to set the voltage. It's pretty nifty, and even has an internal inductor. Efficiency is probably around 90%, and everything was put together on copper sheet. I have 4 more of these ICs, and I am considering selling two for $7 each to make back the shipping money that natsemi charged me. They sure do make nice tube heater supplies though.
Adam Munich, Thu Jun 16 2011, 03:15AM
Well to pass time I started working on the tube head today. Once again the paint is very inconsistent, but this time it actually dried. I used regular rustoleum hammered rather than "universal" rustoleum hammered. Each face of the box has it's own special thing going on, with the top being lumpy, the sides being bumpy and the back being wrinkled/crackled. I give up on making things consistent though, it's just not happening.
[no pic taken...]
For the tube heater I used an adjustable 3A switch mode power supply IC. All you need to do is use one resistor to set the frequency and a resistive divider to set the voltage. It's pretty nifty, and even has an internal inductor. Efficiency is probably around 90%, and everything was put together on copper sheet. I have 4 more of these ICs, and I am considering selling two for $7 each to make back the shipping money that natsemi charged me. They sure do make nice tube heater supplies though.
Re: Grenadier's big thread of Röntgen related shenanigans
magnet18, Thu Jun 16 2011, 03:44AM
What's the number for that IC?
magnet18, Thu Jun 16 2011, 03:44AM
What's the number for that IC?
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Thu Jun 16 2011, 03:55AM
If you order it from national expect to pay $12 and wait 3 weeks.
Adam Munich, Thu Jun 16 2011, 03:55AM
If you order it from national expect to pay $12 and wait 3 weeks.
Re: Grenadier's big thread of Röntgen related shenanigans
magnet18, Thu Jun 16 2011, 04:03AM
Nice, all that, and the bonus that it's EMP proof!! :D
(first page of datasheet)
magnet18, Thu Jun 16 2011, 04:03AM
Nice, all that, and the bonus that it's EMP proof!! :D
(first page of datasheet)
Re: Grenadier's big thread of Röntgen related shenanigans
magnet18, Sun Jul 10 2011, 04:11AM
Got it finished yet?
magnet18, Sun Jul 10 2011, 04:11AM
Got it finished yet?
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Sun Jul 10 2011, 12:09PM
Control box is repaired, just need to build the head when I'm feeling more motivated, and find a sheet of butyl rubber.
Adam Munich, Sun Jul 10 2011, 12:09PM
Control box is repaired, just need to build the head when I'm feeling more motivated, and find a sheet of butyl rubber.
Re: Grenadier's big thread of Röntgen related shenanigans
Xray, Sun Jul 10 2011, 02:47PM
McMaster-Carr Supply
Xray, Sun Jul 10 2011, 02:47PM
Grenadier wrote ...
Control box is repaired, just need to build the head when I'm feeling more motivated, and find a sheet of butyl rubber.
Control box is repaired, just need to build the head when I'm feeling more motivated, and find a sheet of butyl rubber.
McMaster-Carr Supply
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Tue Jul 19 2011, 04:21AM
Decided to start working on this again today, cracked open two vacuum rectifiers and used the bases to make a cable (needs a bit of "finishing" though). Then I plugged it in the sockets and started wiring things up.
HV musth share a common ground with the ucontroller, and it tended to restart the uC when it was turned on. After replacing the mosfet switch with a relay the problem was reduced but not eliminated. I think some sort of NTC thermistor or a large cap after the inductor on the zvs could reduce the voltage spikes that cause things to reset. Or maybe installing the actual cw and x-ray generator could solve the issue (or make it 10x worse).
Managed to blow out the transistor on the linear reg though... have more coming in the mail but that means the project's on hold for a few days.
Adam Munich, Tue Jul 19 2011, 04:21AM
Decided to start working on this again today, cracked open two vacuum rectifiers and used the bases to make a cable (needs a bit of "finishing" though). Then I plugged it in the sockets and started wiring things up.
HV musth share a common ground with the ucontroller, and it tended to restart the uC when it was turned on. After replacing the mosfet switch with a relay the problem was reduced but not eliminated. I think some sort of NTC thermistor or a large cap after the inductor on the zvs could reduce the voltage spikes that cause things to reset. Or maybe installing the actual cw and x-ray generator could solve the issue (or make it 10x worse).
Managed to blow out the transistor on the linear reg though... have more coming in the mail but that means the project's on hold for a few days.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Thu Jul 21 2011, 01:57AM
So... my lipo charger died after I dropped it, cracked the LCD and failed hard at replacing it. Hobbyking is out of lipo chargers and I'm pretty much fuk'd now...
Adam Munich, Thu Jul 21 2011, 01:57AM
So... my lipo charger died after I dropped it, cracked the LCD and failed hard at replacing it. Hobbyking is out of lipo chargers and I'm pretty much fuk'd now...
Re: Grenadier's big thread of Röntgen related shenanigans
magnet18, Thu Jul 21 2011, 02:43AM
If it's any consolation, I overcurrented the nixie driver on my clock and fried it (apparently 12ma is not the same as 20ma...) and I think all the 4017's, and probably all the transistors (one for every freaking number >:()
seems like were in similar boats.
magnet18, Thu Jul 21 2011, 02:43AM
If it's any consolation, I overcurrented the nixie driver on my clock and fried it (apparently 12ma is not the same as 20ma...) and I think all the 4017's, and probably all the transistors (one for every freaking number >:()
seems like were in similar boats.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Sat Jul 30 2011, 05:57PM
The cable is done. It's a bit short at 4 feet though... ran out of wire. When I get some more wire (and 2 more tube sockets) I will make a longer cable, maybe 15 feet. In the meantime I'll just press expose and walk away while the timer counts down for a few seconds.
Pretty satisfied with it. The wrapped string and octal bases give it the 'old' look I was going for. JB weld secures the wires in the bases.
Now I went to paint the last part (tubehead lid) yesterday, but seems like I bought some faulty paint because it failed to hammer. Returned the can and got a new one, and once the crappy layer is done curing (tomorrow) I'll try a new coat.
Adam Munich, Sat Jul 30 2011, 05:57PM
The cable is done. It's a bit short at 4 feet though... ran out of wire. When I get some more wire (and 2 more tube sockets) I will make a longer cable, maybe 15 feet. In the meantime I'll just press expose and walk away while the timer counts down for a few seconds.
Pretty satisfied with it. The wrapped string and octal bases give it the 'old' look I was going for. JB weld secures the wires in the bases.
Now I went to paint the last part (tubehead lid) yesterday, but seems like I bought some faulty paint because it failed to hammer. Returned the can and got a new one, and once the crappy layer is done curing (tomorrow) I'll try a new coat.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Sat Aug 06 2011, 05:56PM
Hey guess what it works!
<< Dosimetry Video
Well it did work... until I borked it.
The x-ray was working just fine until I decided to add a little capacitance to the ZVS. It was my hope that this would lower the resonant frequency and impedance, and allow more current to flow in the ZVS. It did, and I got 500uA more in the coolidge tube. I then decided to add a bit more capacitance, and that killed it.
Here is what I think happened based on the damage; When the relay turned off the ZVS, the larger currents did not want to stop flowing and a small arc formed in the switch. In order to sustain the arc the LC tank raised its voltage, and since I'm a dumbass I put the TVS diode on the relay side after 4 feet of cable. Because of that it did jack shit, and the higher voltages over by the ZVS punched through the mosfets' gate and latched them on. This exploded the large voltage regulator and shorted out the battery, and since that is a LiPo about 300 amps flowed for a few milliseconds. When the fuse burned out, another inductively fed arc formed inside there and that caused a high voltage on the 14.4V rail. This burned out the 5 volt buck converter, and let 14.4V flow into all the microelectronics, thus popping every bit of silicon in the system. Including the nixie tube boost converter. The EL wire inverter also exploded, so I have to wait for the mail for another one of those. The *only* thing that did not explode was the buck converter that powers the x-ray tube's heater, and I'm dumbfounded at how robust it is.
I decided to bypass the microelectronics and just connect power to the zvs with long wires. It failed to work. The power was there, the mAmeter pegged and there was no kilovolts. Uh oh...
After drawing an arc from the unheated tube I came to the conclusion it was gassy. Well... what do I expect for such a cheap tube. It's a wonder anything works in china! I'm going to replace it with a CEI tube, and being made in italy that thing should be a hell of a lot more robust.
Now what to do with the gassy tube... I'm thinking nightlight or flashlight, seeing as the heater is still OK.
Adam Munich, Sat Aug 06 2011, 05:56PM
Hey guess what it works!
<< Dosimetry VideoWell it did work... until I borked it.
The x-ray was working just fine until I decided to add a little capacitance to the ZVS. It was my hope that this would lower the resonant frequency and impedance, and allow more current to flow in the ZVS. It did, and I got 500uA more in the coolidge tube. I then decided to add a bit more capacitance, and that killed it.
Here is what I think happened based on the damage; When the relay turned off the ZVS, the larger currents did not want to stop flowing and a small arc formed in the switch. In order to sustain the arc the LC tank raised its voltage, and since I'm a dumbass I put the TVS diode on the relay side after 4 feet of cable. Because of that it did jack shit, and the higher voltages over by the ZVS punched through the mosfets' gate and latched them on. This exploded the large voltage regulator and shorted out the battery, and since that is a LiPo about 300 amps flowed for a few milliseconds. When the fuse burned out, another inductively fed arc formed inside there and that caused a high voltage on the 14.4V rail. This burned out the 5 volt buck converter, and let 14.4V flow into all the microelectronics, thus popping every bit of silicon in the system. Including the nixie tube boost converter. The EL wire inverter also exploded, so I have to wait for the mail for another one of those. The *only* thing that did not explode was the buck converter that powers the x-ray tube's heater, and I'm dumbfounded at how robust it is.
I decided to bypass the microelectronics and just connect power to the zvs with long wires. It failed to work. The power was there, the mAmeter pegged and there was no kilovolts. Uh oh...
After drawing an arc from the unheated tube I came to the conclusion it was gassy. Well... what do I expect for such a cheap tube. It's a wonder anything works in china! I'm going to replace it with a CEI tube, and being made in italy that thing should be a hell of a lot more robust.
Now what to do with the gassy tube... I'm thinking nightlight or flashlight, seeing as the heater is still OK.
Re: Grenadier's big thread of Röntgen related shenanigans
Proud Mary, Sat Aug 06 2011, 06:14PM
What 'seasoning' regime did you use with the new Chinese tube, Adam?
I don't understand the role of 'drawing arcs' in determining the status of an X-ray tube.
Aren't most of the world's electronic components made in China?
Proud Mary, Sat Aug 06 2011, 06:14PM
Grenadier wrote ...
After drawing an arc from the unheated tube I came to the conclusion it was gassy. Well... what do I expect for such a cheap tube. It's a wonder anything works in china! I'm going to replace it with a CEI tube, and being made in italy that thing should be a hell of a lot more robust.
Now what to do with the gassy tube... I'm thinking nightlight or flashlight, seeing as the heater is still OK.
After drawing an arc from the unheated tube I came to the conclusion it was gassy. Well... what do I expect for such a cheap tube. It's a wonder anything works in china! I'm going to replace it with a CEI tube, and being made in italy that thing should be a hell of a lot more robust.
Now what to do with the gassy tube... I'm thinking nightlight or flashlight, seeing as the heater is still OK.
What 'seasoning' regime did you use with the new Chinese tube, Adam?
I don't understand the role of 'drawing arcs' in determining the status of an X-ray tube.
Aren't most of the world's electronic components made in China?
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Sat Aug 06 2011, 08:43PM
I followed this guide:
After taking apart the tubehead, it turns out that the HV punched right through the tube. This was one of my initial concerns, because of the conductive lead shielding and the thin glass. I compensated for this by putting oil between the lead and the tube, but when the heater cut out the oil stood no chance against the increased voltage.
I'm not really crying though. This tube wasn't the best of quality anyway and judging by the burn mark on the anode, its focal spot was 1.5mm (though it was *supposed* to be only .7mm).
This CEI tube I'm going to use is bigger, has thicker glass and a .5mm focal spot. It's an all around better tube, and should provide all around better images.
When I rebuild it I'm also going to make sure that the HV cuts out if the heater does. Should have done that in the first place...
Also going to insulate the tube from the lead better.
Adam Munich, Sat Aug 06 2011, 08:43PM
I followed this guide:
After taking apart the tubehead, it turns out that the HV punched right through the tube. This was one of my initial concerns, because of the conductive lead shielding and the thin glass. I compensated for this by putting oil between the lead and the tube, but when the heater cut out the oil stood no chance against the increased voltage.
I'm not really crying though. This tube wasn't the best of quality anyway and judging by the burn mark on the anode, its focal spot was 1.5mm (though it was *supposed* to be only .7mm).
This CEI tube I'm going to use is bigger, has thicker glass and a .5mm focal spot. It's an all around better tube, and should provide all around better images.
When I rebuild it I'm also going to make sure that the HV cuts out if the heater does. Should have done that in the first place...
Also going to insulate the tube from the lead better.
Re: Grenadier's big thread of Röntgen related shenanigans
Proud Mary, Sat Aug 06 2011, 11:05PM
Still, it's always a shame to lose expensive parts.
I'd suggest having a minimum of 25mm between the glass envelope and the shielding
(a) to assist convection cooling of the glass by the dielectric oil
(b) to keep down the capacitance between the internal electrodes and the shielding, which alone could provoke a glass strike.
No doubt someone will step in and say such a wide spacing is unnecessary, but then they won't be the ones paying the replacement cost, and waiting who knows how long for new parts to arrive in the post.
I suggest as minimum HV lock-out features:
(1) Heater must have been running for 5 minutes before HV can be applied.
(2) HV will auto-disconnect in the event of heater current falling below I mA
(3) HV will auto-disconnect if an attempt is made to open the case during operation - as per microwave oven.
On focal spots: the area of anode erosion will always be larger than the focal spot itself, because heat travels outward from the impacted zone. The standard way to measure the focal spot size uses simple geometry based on careful pin-hole imaging - a skill well worth the trouble of learning how to do well.
The focal spot size, definition, and symmetry will deteriorate over time as the impacted zone starts to pit and crack.
You should also ask yourself how much your focal spot may be deflected, modified, or enlarged by unstable off-axis electric fields inside the casing.
Proud Mary, Sat Aug 06 2011, 11:05PM
Grenadier wrote ...
I followed this guide:
After taking apart the tubehead, it turns out that the HV punched right through the tube. This was one of my initial concerns, because of the conductive lead shielding and the thin glass. I compensated for this by putting oil between the lead and the tube, but when the heater cut out the oil stood no chance against the increased voltage.
I'm not really crying though. This tube wasn't the best of quality anyway and judging by the burn mark on the anode, its focal spot was 1.5mm (though it was *supposed* to be only .7mm).
This CEI tube I'm going to use is bigger, has thicker glass and a .5mm focal spot. It's an all around better tube, and should provide all around better images.
When I rebuild it I'm also going to make sure that the HV cuts out if the heater does. Should have done that in the first place...
Also going to insulate the tube from the lead better.
I followed this guide:
After taking apart the tubehead, it turns out that the HV punched right through the tube. This was one of my initial concerns, because of the conductive lead shielding and the thin glass. I compensated for this by putting oil between the lead and the tube, but when the heater cut out the oil stood no chance against the increased voltage.
I'm not really crying though. This tube wasn't the best of quality anyway and judging by the burn mark on the anode, its focal spot was 1.5mm (though it was *supposed* to be only .7mm).
This CEI tube I'm going to use is bigger, has thicker glass and a .5mm focal spot. It's an all around better tube, and should provide all around better images.
When I rebuild it I'm also going to make sure that the HV cuts out if the heater does. Should have done that in the first place...
Also going to insulate the tube from the lead better.
Still, it's always a shame to lose expensive parts.
I'd suggest having a minimum of 25mm between the glass envelope and the shielding
(a) to assist convection cooling of the glass by the dielectric oil
(b) to keep down the capacitance between the internal electrodes and the shielding, which alone could provoke a glass strike.
No doubt someone will step in and say such a wide spacing is unnecessary, but then they won't be the ones paying the replacement cost, and waiting who knows how long for new parts to arrive in the post.
I suggest as minimum HV lock-out features:
(1) Heater must have been running for 5 minutes before HV can be applied.
(2) HV will auto-disconnect in the event of heater current falling below I mA
(3) HV will auto-disconnect if an attempt is made to open the case during operation - as per microwave oven.
On focal spots: the area of anode erosion will always be larger than the focal spot itself, because heat travels outward from the impacted zone. The standard way to measure the focal spot size uses simple geometry based on careful pin-hole imaging - a skill well worth the trouble of learning how to do well.
The focal spot size, definition, and symmetry will deteriorate over time as the impacted zone starts to pit and crack.
You should also ask yourself how much your focal spot may be deflected, modified, or enlarged by unstable off-axis electric fields inside the casing.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Sat Aug 06 2011, 11:17PM
I don't have enough room for such spacing in there. From all the X-ray heads I've taken apart though, the tube jacket is never more than 1cm away from the tube, and often it's <5mm.
I have a few tubes to choose from. One is the CEI-OCX-70G, another tube is the TRX-708 from kodak. Both tubes have their anodes embedded in the copper block to block off axis radiation. The TRX-708 has a nicer anode hole (and would make a rounder beam) than the CEI one, but the focal spot seems to be a line rather than a spot.
The OCX-70G has a control grid, but I don't need it so I'm likely just going to leave it disconnected if I use that tube. I also have an OCX-65G, but that one isn't new while my 70G is.
I also have another tube, one that is clearly used but has a perfect anode. No markings on it however.
I have a tube shield too, Two actually. One of them has a lead sheath with a ceramic "inside part (insulator maybe)", while the other is the same but with a phenolic tube insulator. I plan on using one of those instead of a handmade shield.
Adam Munich, Sat Aug 06 2011, 11:17PM
I don't have enough room for such spacing in there. From all the X-ray heads I've taken apart though, the tube jacket is never more than 1cm away from the tube, and often it's <5mm.
I have a few tubes to choose from. One is the CEI-OCX-70G, another tube is the TRX-708 from kodak. Both tubes have their anodes embedded in the copper block to block off axis radiation. The TRX-708 has a nicer anode hole (and would make a rounder beam) than the CEI one, but the focal spot seems to be a line rather than a spot.
The OCX-70G has a control grid, but I don't need it so I'm likely just going to leave it disconnected if I use that tube. I also have an OCX-65G, but that one isn't new while my 70G is.
I also have another tube, one that is clearly used but has a perfect anode. No markings on it however.
I have a tube shield too, Two actually. One of them has a lead sheath with a ceramic "inside part (insulator maybe)", while the other is the same but with a phenolic tube insulator. I plan on using one of those instead of a handmade shield.
Re: Grenadier's big thread of Röntgen related shenanigans
Proud Mary, Sat Aug 06 2011, 11:28PM
But they didn't use your chaotic power supply, did they?
And if they were dental or fixed anode medical radiography heads, how long would a typical exposure be? A few hundred milliseconds? less? - you will have to think about cooling in general - and the datasheet figure for the heat capacity of the anode in particular - if your tube is to survive many seconds of continuous use in your video experiments.
Proud Mary, Sat Aug 06 2011, 11:28PM
Grenadier wrote ...
I don't have enough room for such spacing in there. From all the X-ray heads I've taken apart though, the tube jacket is never more than 1cm away from the tube, and often it's <5mm.
I don't have enough room for such spacing in there. From all the X-ray heads I've taken apart though, the tube jacket is never more than 1cm away from the tube, and often it's <5mm.
But they didn't use your chaotic power supply, did they?
And if they were dental or fixed anode medical radiography heads, how long would a typical exposure be? A few hundred milliseconds? less? - you will have to think about cooling in general - and the datasheet figure for the heat capacity of the anode in particular - if your tube is to survive many seconds of continuous use in your video experiments.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Sat Aug 06 2011, 11:44PM
True, but my power supply isn't supposed to be chaotic. My mistake was not putting in the HV kill when the power to the heater was inadvertently cut.
I think I'm going to use the 70G for this. I fit it inside the phenolic tube insulated shield with some hose and soon a small dab of epoxy. This tube has the anode "arm" recessed a bit inside the glass, so I am going to slide a platic tube in there to prevent sparking to the shield in case of failure.
The tube has a .7mm focal spot and a 10kJ heat storage capacity. Sure tubes in commercial sets don't run long, but they are running at 500+ watts while I'll run mine at no more than 130W.
So now I just need to wait for a new EL wire inverter and then I can put this back together. I'm going to order a huge amount of 5.1V zener diodes, 18V zeners and 40V zeners to protect all the power rails. I'll also add some 3.1V zeners across the heater to protect the buck converter there.
Oddly enough, that buck converter is the only thing I haven't been able to blow up, and I expected it to be the most fragile thing. It's right next to the HV both physically and electrically... Idunno.
Only thing that I can't do anything about really, if the buck converter there fails then the tube will have no heater. I can clamp the voltage at 5.5V (to protect the heater) until a fuse on the heater blows, but that's about it.
Hrm... now that I think about it, I might be able to do some clever rewiring that kills both the HV and the heater if that fuse + buck blows. Well maybe not... both use different currents. Ah, but I can ground the ZVS relay *after* the fuse. That will kill both if something goes wrong
Adam Munich, Sat Aug 06 2011, 11:44PM
True, but my power supply isn't supposed to be chaotic. My mistake was not putting in the HV kill when the power to the heater was inadvertently cut.
I think I'm going to use the 70G for this. I fit it inside the phenolic tube insulated shield with some hose and soon a small dab of epoxy. This tube has the anode "arm" recessed a bit inside the glass, so I am going to slide a platic tube in there to prevent sparking to the shield in case of failure.
The tube has a .7mm focal spot and a 10kJ heat storage capacity. Sure tubes in commercial sets don't run long, but they are running at 500+ watts while I'll run mine at no more than 130W.
So now I just need to wait for a new EL wire inverter and then I can put this back together. I'm going to order a huge amount of 5.1V zener diodes, 18V zeners and 40V zeners to protect all the power rails. I'll also add some 3.1V zeners across the heater to protect the buck converter there.
Oddly enough, that buck converter is the only thing I haven't been able to blow up, and I expected it to be the most fragile thing. It's right next to the HV both physically and electrically... Idunno.
Only thing that I can't do anything about really, if the buck converter there fails then the tube will have no heater. I can clamp the voltage at 5.5V (to protect the heater) until a fuse on the heater blows, but that's about it.
Hrm... now that I think about it, I might be able to do some clever rewiring that kills both the HV and the heater if that fuse + buck blows. Well maybe not... both use different currents. Ah, but I can ground the ZVS relay *after* the fuse. That will kill both if something goes wrong
Re: Grenadier's big thread of Röntgen related shenanigans
Xray, Sun Aug 07 2011, 12:32AM
The actual focal spot size that you see on the target of an X-ray tube is not the nominal focal spot that you read in the data sheet for that specific tube. The data sheet refers to the "effective" focal spot size, which is the focal spot that the imaging film or digital sensor "sees", due to the angle of the target. Most dental and medical X-ray tubes use the "line focus principle" technique where the filament is typically much longer than it is wide, and therefore produces an etch or burn mark on the Tungsten target which is long and thin (in your case it is 1.5mm long). Here's a good way to visualize how the line focus principle works. Imagine a 12-inch ruler floating vertically about a couple of feet in front of your face, with the center exactly in line with your eyes. The ruler of course looks to be 12 inches long. Now imagine that someone rotates the ruler so that the upper 6 inches now slopes away from your face, and the lower 6 inches slopes toward your face, and they rotated it exactly 45 degrees from its initial position. Now, the ruler no longer appears to be 12 inches long to your eyes! It will appear to be 12 * sin(45) = 8.49 inches long! So, the actual length is still 12 inches, but the effective length is much shorter. That's the basics of how line focus works with X-ray tubes. Depending on the focal spot length to width ratio, and the angle of the anode (target), the effective focal spot might appear to be a tiny square dot, even though the filament is long and skinny!
Xray, Sun Aug 07 2011, 12:32AM
Grenadier wrote ...
I'm not really crying though. This tube wasn't the best of quality anyway and judging by the burn mark on the anode, its focal spot was 1.5mm (though it was *supposed* to be only .7mm).
I'm not really crying though. This tube wasn't the best of quality anyway and judging by the burn mark on the anode, its focal spot was 1.5mm (though it was *supposed* to be only .7mm).
The actual focal spot size that you see on the target of an X-ray tube is not the nominal focal spot that you read in the data sheet for that specific tube. The data sheet refers to the "effective" focal spot size, which is the focal spot that the imaging film or digital sensor "sees", due to the angle of the target. Most dental and medical X-ray tubes use the "line focus principle" technique where the filament is typically much longer than it is wide, and therefore produces an etch or burn mark on the Tungsten target which is long and thin (in your case it is 1.5mm long). Here's a good way to visualize how the line focus principle works. Imagine a 12-inch ruler floating vertically about a couple of feet in front of your face, with the center exactly in line with your eyes. The ruler of course looks to be 12 inches long. Now imagine that someone rotates the ruler so that the upper 6 inches now slopes away from your face, and the lower 6 inches slopes toward your face, and they rotated it exactly 45 degrees from its initial position. Now, the ruler no longer appears to be 12 inches long to your eyes! It will appear to be 12 * sin(45) = 8.49 inches long! So, the actual length is still 12 inches, but the effective length is much shorter. That's the basics of how line focus works with X-ray tubes. Depending on the focal spot length to width ratio, and the angle of the anode (target), the effective focal spot might appear to be a tiny square dot, even though the filament is long and skinny!
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Sun Aug 07 2011, 01:11AM
I see that, but looking directly into the anode hole of that tube you could see that the burn mark was taller than it was wider, and it was a line, even from that POV. I think that tube might just be messed up or something.
If only I could fit this one in the case...
Adam Munich, Sun Aug 07 2011, 01:11AM
I see that, but looking directly into the anode hole of that tube you could see that the burn mark was taller than it was wider, and it was a line, even from that POV. I think that tube might just be messed up or something.
If only I could fit this one in the case...
Re: Grenadier's big thread of Röntgen related shenanigans
Proud Mary, Sun Aug 07 2011, 01:28AM
You're doing very well. Your persistence with this project over many months does you credit!
I'm pleased that friend "X-ray" has popped up to advise you, because I have very little practical experience with medical tubes and their particular HV needs to share with you. The world looks very different below 5 keV, where I have staked my claim.
Proud Mary, Sun Aug 07 2011, 01:28AM
Grenadier wrote ...
True, but my power supply isn't supposed to be chaotic. My mistake was not putting in the HV kill when the power to the heater was inadvertently cut.
I think I'm going to use the 70G for this. I fit it inside the phenolic tube insulated shield with some hose and soon a small dab of epoxy. This tube has the anode "arm" recessed a bit inside the glass, so I am going to slide a platic tube in there to prevent sparking to the shield in case of failure.
The tube has a .7mm focal spot and a 10kJ heat storage capacity. Sure tubes in commercial sets don't run long, but they are running at 500+ watts while I'll run mine at no more than 130W.
So now I just need to wait for a new EL wire inverter and then I can put this back together. I'm going to order a huge amount of 5.1V zener diodes, 18V zeners and 40V zeners to protect all the power rails. I'll also add some 3.1V zeners across the heater to protect the buck converter there.
Oddly enough, that buck converter is the only thing I haven't been able to blow up, and I expected it to be the most fragile thing. It's right next to the HV both physically and electrically... Idunno.
Only thing that I can't do anything about really, if the buck converter there fails then the tube will have no heater. I can clamp the voltage at 5.5V (to protect the heater) until a fuse on the heater blows, but that's about it.
Hrm... now that I think about it, I might be able to do some clever rewiring that kills both the HV and the heater if that fuse + buck blows. Well maybe not... both use different currents. Ah, but I can ground the ZVS relay *after* the fuse. That will kill both if something goes wrong
True, but my power supply isn't supposed to be chaotic. My mistake was not putting in the HV kill when the power to the heater was inadvertently cut.
I think I'm going to use the 70G for this. I fit it inside the phenolic tube insulated shield with some hose and soon a small dab of epoxy. This tube has the anode "arm" recessed a bit inside the glass, so I am going to slide a platic tube in there to prevent sparking to the shield in case of failure.
The tube has a .7mm focal spot and a 10kJ heat storage capacity. Sure tubes in commercial sets don't run long, but they are running at 500+ watts while I'll run mine at no more than 130W.
So now I just need to wait for a new EL wire inverter and then I can put this back together. I'm going to order a huge amount of 5.1V zener diodes, 18V zeners and 40V zeners to protect all the power rails. I'll also add some 3.1V zeners across the heater to protect the buck converter there.
Oddly enough, that buck converter is the only thing I haven't been able to blow up, and I expected it to be the most fragile thing. It's right next to the HV both physically and electrically... Idunno.
Only thing that I can't do anything about really, if the buck converter there fails then the tube will have no heater. I can clamp the voltage at 5.5V (to protect the heater) until a fuse on the heater blows, but that's about it.
Hrm... now that I think about it, I might be able to do some clever rewiring that kills both the HV and the heater if that fuse + buck blows. Well maybe not... both use different currents. Ah, but I can ground the ZVS relay *after* the fuse. That will kill both if something goes wrong
You're doing very well. Your persistence with this project over many months does you credit!
I'm pleased that friend "X-ray" has popped up to advise you, because I have very little practical experience with medical tubes and their particular HV needs to share with you. The world looks very different below 5 keV, where I have staked my claim.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Sun Aug 07 2011, 03:38AM
Heh, yeah too bad things keep exploding. >_<
After this is done I want to make a second head for this machine, one with a low energy x-ray tube. This head is [was] only capable of energies down to about 40keV, so I'd need a second head to take images of soft things like flowers. Unfortunately all of my tubes are thick glass, and are thus incapable of making decent quantities of low energy x-rays.
I've had no luck finding a beryllium or aluminum window x-ray tube anywhere
Adam Munich, Sun Aug 07 2011, 03:38AM
Heh, yeah too bad things keep exploding. >_<
After this is done I want to make a second head for this machine, one with a low energy x-ray tube. This head is [was] only capable of energies down to about 40keV, so I'd need a second head to take images of soft things like flowers. Unfortunately all of my tubes are thick glass, and are thus incapable of making decent quantities of low energy x-rays.
I've had no luck finding a beryllium or aluminum window x-ray tube anywhere
Re: Grenadier's big thread of Röntgen related shenanigans
Proud Mary, Sun Aug 07 2011, 09:29AM
Proud Mary, Sun Aug 07 2011, 09:29AM
Grenadier wrote ...
I've had no luck finding a beryllium or aluminum window x-ray tube anywhere
I've had no luck finding a beryllium or aluminum window x-ray tube anywhere
Re: Grenadier's big thread of Röntgen related shenanigans
Xray, Sun Aug 07 2011, 05:20PM
All X-ray tubeheads used for X-raying living tissue have metallic (usually aluminum) filters directly in the path of the raw beam as it exits the tubehead. The filters attenuate the lower portion of the energy spectrum, which is too weak to produce a useful image, but can burn the skin. Because you will not be X-raying living tissue, you do not need filtration, and if you can reduce the amount of oil that's between the glass X-ray tube and the exit window, you should be able to get decent low-energy photons from it.
I have a couple of very small tubes (about the size of a large walnut) that have a portion of the thick glass ground down to a thin glass window. The thin glass may not be as transparent to X-rays as beryllium is, but it should work just fine for X-raying flowers and seashells, etc. Let me know if you want one of them and maybe we can work out a trade.
Xray, Sun Aug 07 2011, 05:20PM
Grenadier wrote ...
Unfortunately all of my tubes are thick glass, and are thus incapable of making decent quantities of low energy x-rays.
I've had no luck finding a beryllium or aluminum window x-ray tube anywhere
Unfortunately all of my tubes are thick glass, and are thus incapable of making decent quantities of low energy x-rays.
I've had no luck finding a beryllium or aluminum window x-ray tube anywhere
All X-ray tubeheads used for X-raying living tissue have metallic (usually aluminum) filters directly in the path of the raw beam as it exits the tubehead. The filters attenuate the lower portion of the energy spectrum, which is too weak to produce a useful image, but can burn the skin. Because you will not be X-raying living tissue, you do not need filtration, and if you can reduce the amount of oil that's between the glass X-ray tube and the exit window, you should be able to get decent low-energy photons from it.
I have a couple of very small tubes (about the size of a large walnut) that have a portion of the thick glass ground down to a thin glass window. The thin glass may not be as transparent to X-rays as beryllium is, but it should work just fine for X-raying flowers and seashells, etc. Let me know if you want one of them and maybe we can work out a trade.
Re: Grenadier's big thread of Röntgen related shenanigans
magnet18, Mon Aug 08 2011, 06:08AM
While you're waiting around for parts, I'd love to see some pictures/video of the assembled case with nixies and everything
I'm considering using that hammered paint on my nixie clock
(If I can figure out why I keep frying power supplies :P)
magnet18, Mon Aug 08 2011, 06:08AM
While you're waiting around for parts, I'd love to see some pictures/video of the assembled case with nixies and everything
I'm considering using that hammered paint on my nixie clock
(If I can figure out why I keep frying power supplies :P)
Re: Grenadier's big thread of Röntgen related shenanigans
Proud Mary, Mon Aug 08 2011, 08:35AM
15 keV would be a good place to start for someone interested in the low energy end of the spectrum, because some ordinary off-the-shelf detection and measurement equipment and techniques can still be used here. For example, mica end-window GM tubes and home-made Al window ionisation chambers can still be expected to produce a signal.
Proud Mary, Mon Aug 08 2011, 08:35AM
Xray wrote ...
I have a couple of very small tubes (about the size of a large walnut) that have a portion of the thick glass ground down to a thin glass window. The thin glass may not be as transparent to X-rays as beryllium is, but it should work just fine for X-raying flowers and seashells, etc. Let me know if you want one of them and maybe we can work out a trade.
I have a couple of very small tubes (about the size of a large walnut) that have a portion of the thick glass ground down to a thin glass window. The thin glass may not be as transparent to X-rays as beryllium is, but it should work just fine for X-raying flowers and seashells, etc. Let me know if you want one of them and maybe we can work out a trade.
15 keV would be a good place to start for someone interested in the low energy end of the spectrum, because some ordinary off-the-shelf detection and measurement equipment and techniques can still be used here. For example, mica end-window GM tubes and home-made Al window ionisation chambers can still be expected to produce a signal.
Re: Grenadier's big thread of Röntgen related shenanigans
klugesmith, Mon Aug 08 2011, 05:23PM
Anode heat capacity is a _critical_ limit, especially since I think the screen luminance per HV watt goes down much faster than the anode voltage. Look up the meaning of "heat unit" as found in Coolidge tube datasheets. My next version will have a heatsink and/or oil around the anode terminal of the tube, even though HV insulation is not a problem at these voltages.
Oh, and I'm not going to skip the home-made ionization chamber. Starting with an off-the-shelf picoammeter will save some soldering time. 9V batteries in series can provide more than enough bias voltage. My metal-windowed Geiger counter responds strongly even at half of the NST voltage, so by silence it indicates when shielding & distance are adequate for safety. (Or that the X-ray source or Geiger counter are off, or broken.)
klugesmith, Mon Aug 08 2011, 05:23PM
Proud Mary wrote ...
15 keV would be a good place to start for someone interested in the low energy end of the spectrum, because some ordinary off-the-shelf detection and measurement equipment and techniques can still be used here. For example, mica end-window GM tubes and home-made Al window ionisation chambers can still be expected to produce a signal.
When I get back to the x-ray hobby, am planning to continue using my nominal 15 kV NST, before firing up an XRT bought from x-ray. Can attest that NST and an unthinned-glass dental tube, and no oil, can produce nice shadows of thin aluminum soda cans, and little plastic hotel-shampoo bottles. (The shampoo attenuates these x-rays more than it attenuates light.)Xray wrote ...
I have a couple of very small tubes (about the size of a large walnut) that have a portion of the thick glass ground down to a thin glass window. The thin glass may not be as transparent to X-rays as beryllium is, but it should work just fine for X-raying flowers and seashells, etc. Let me know if you want one of them and maybe we can work out a trade.
I have a couple of very small tubes (about the size of a large walnut) that have a portion of the thick glass ground down to a thin glass window. The thin glass may not be as transparent to X-rays as beryllium is, but it should work just fine for X-raying flowers and seashells, etc. Let me know if you want one of them and maybe we can work out a trade.
15 keV would be a good place to start for someone interested in the low energy end of the spectrum, because some ordinary off-the-shelf detection and measurement equipment and techniques can still be used here. For example, mica end-window GM tubes and home-made Al window ionisation chambers can still be expected to produce a signal.
Anode heat capacity is a _critical_ limit, especially since I think the screen luminance per HV watt goes down much faster than the anode voltage. Look up the meaning of "heat unit" as found in Coolidge tube datasheets. My next version will have a heatsink and/or oil around the anode terminal of the tube, even though HV insulation is not a problem at these voltages.
Oh, and I'm not going to skip the home-made ionization chamber. Starting with an off-the-shelf picoammeter will save some soldering time. 9V batteries in series can provide more than enough bias voltage. My metal-windowed Geiger counter responds strongly even at half of the NST voltage, so by silence it indicates when shielding & distance are adequate for safety. (Or that the X-ray source or Geiger counter are off, or broken.)
Re: Grenadier's big thread of Röntgen related shenanigans
Xray, Mon Aug 08 2011, 06:10PM
When I read that you may use a heatsink on your X-ray tube, it reminded me of an old dental tube head that was made by Weber X-ray which used Sulfur Hexafluoride (SF6) gas as the hv insulation and heat sink. It was the ONLY dental tube head (to my knowledge) that used SF6 instead of oil. The X-ray tube had a ribbed aluminum heatsink clamped to the anode shank, and was fed hv from a split transformer that supplied 35KV AC to the anode, and 35KV AC (opposite phase) to the cathode. I believe that the gas was under light pressure (maybe 2 or 3 atmospheres). I've had a couple of those heads come into my shop many years ago, but I did not have the proper equipment that was necessary to replace the lost gas after opening the head to repair it. But I got to see how that head was made.
I don't know how difficult or practical it would be to get SF6 gas for hobbyist use, but it would be an interesting project if someone were to make an X-ray head that was insulated with SF6! I know that SF6 is a very dense "greenhouse gas", so there may be very strict EPA rules and regulations that apply to its sale, storage, and use. Electrical power distribution companies use it in many of their hv circuit breakers and other hv components, but I believe that it's being phased out because of its negative impact on the environment.
Xray, Mon Aug 08 2011, 06:10PM
Klugesmith wrote ...
My next version will have a heatsink and/or oil around the anode terminal of the tube, even though HV insulation is not a problem at these voltages.
My next version will have a heatsink and/or oil around the anode terminal of the tube, even though HV insulation is not a problem at these voltages.
When I read that you may use a heatsink on your X-ray tube, it reminded me of an old dental tube head that was made by Weber X-ray which used Sulfur Hexafluoride (SF6) gas as the hv insulation and heat sink. It was the ONLY dental tube head (to my knowledge) that used SF6 instead of oil. The X-ray tube had a ribbed aluminum heatsink clamped to the anode shank, and was fed hv from a split transformer that supplied 35KV AC to the anode, and 35KV AC (opposite phase) to the cathode. I believe that the gas was under light pressure (maybe 2 or 3 atmospheres). I've had a couple of those heads come into my shop many years ago, but I did not have the proper equipment that was necessary to replace the lost gas after opening the head to repair it. But I got to see how that head was made.
I don't know how difficult or practical it would be to get SF6 gas for hobbyist use, but it would be an interesting project if someone were to make an X-ray head that was insulated with SF6! I know that SF6 is a very dense "greenhouse gas", so there may be very strict EPA rules and regulations that apply to its sale, storage, and use. Electrical power distribution companies use it in many of their hv circuit breakers and other hv components, but I believe that it's being phased out because of its negative impact on the environment.
Re: Grenadier's big thread of Röntgen related shenanigans
Proud Mary, Mon Aug 08 2011, 06:18PM
I'm sure a good many hastily assembled X-ray experiments dissapoint because too much attention has been paid to ever higher voltage, without thought to the consequences of high PSU output impedance, with the result that the anode voltage falls flat on its face as soon as the tube starts to draw current. Much better to see what can be done with a steady but modest supply like your 15 kV NST where you know what you're getting, and effective shielding is easy to implement, not of unmanageable weight, and is inexpensive.
Whilst only a small minority of photons of 15 keV will be produced at 15 kVp, most of those that are can reach out ten feet through the air to strike the clueless and the negligent:
Proud Mary, Mon Aug 08 2011, 06:18PM
Klugesmith wrote ...
Anode heat capacity is a _critical_ limit, especially since I think the screen luminance per HV watt goes down much faster than the anode voltage. Look up the meaning of "heat unit" as found in Coolidge tube datasheets. My next version will have a heatsink and/or oil around the anode terminal of the tube, even though HV insulation is not a problem at these voltages.
Oh, and I'm not going to skip the home-made ionization chamber. Starting with an off-the-shelf picoammeter will save some soldering time. 9V batteries in series can provide more than enough bias voltage. My metal-windowed Geiger counter responds strongly even at half of the NST voltage, so by silence it indicates when shielding & distance are adequate for safety. (Or that the X-ray source or Geiger counter are off, or broken.)
Proud Mary wrote ...
15 keV would be a good place to start for someone interested in the low energy end of the spectrum, because some ordinary off-the-shelf detection and measurement equipment and techniques can still be used here. For example, mica end-window GM tubes and home-made Al window ionisation chambers can still be expected to produce a signal.
When I get back to the x-ray hobby, am planning to continue using my nominal 15 kV NST, before firing up an XRT bought from x-ray. Can attest that NST and an unthinned-glass dental tube, and no oil, can produce nice shadows of thin aluminum soda cans, and little plastic hotel-shampoo bottles. (The shampoo attenuates these x-rays more than it attenuates light.)Xray wrote ...
I have a couple of very small tubes (about the size of a large walnut) that have a portion of the thick glass ground down to a thin glass window. The thin glass may not be as transparent to X-rays as beryllium is, but it should work just fine for X-raying flowers and seashells, etc. Let me know if you want one of them and maybe we can work out a trade.
I have a couple of very small tubes (about the size of a large walnut) that have a portion of the thick glass ground down to a thin glass window. The thin glass may not be as transparent to X-rays as beryllium is, but it should work just fine for X-raying flowers and seashells, etc. Let me know if you want one of them and maybe we can work out a trade.
15 keV would be a good place to start for someone interested in the low energy end of the spectrum, because some ordinary off-the-shelf detection and measurement equipment and techniques can still be used here. For example, mica end-window GM tubes and home-made Al window ionisation chambers can still be expected to produce a signal.
Anode heat capacity is a _critical_ limit, especially since I think the screen luminance per HV watt goes down much faster than the anode voltage. Look up the meaning of "heat unit" as found in Coolidge tube datasheets. My next version will have a heatsink and/or oil around the anode terminal of the tube, even though HV insulation is not a problem at these voltages.
Oh, and I'm not going to skip the home-made ionization chamber. Starting with an off-the-shelf picoammeter will save some soldering time. 9V batteries in series can provide more than enough bias voltage. My metal-windowed Geiger counter responds strongly even at half of the NST voltage, so by silence it indicates when shielding & distance are adequate for safety. (Or that the X-ray source or Geiger counter are off, or broken.)
I'm sure a good many hastily assembled X-ray experiments dissapoint because too much attention has been paid to ever higher voltage, without thought to the consequences of high PSU output impedance, with the result that the anode voltage falls flat on its face as soon as the tube starts to draw current. Much better to see what can be done with a steady but modest supply like your 15 kV NST where you know what you're getting, and effective shielding is easy to implement, not of unmanageable weight, and is inexpensive.
Whilst only a small minority of photons of 15 keV will be produced at 15 kVp, most of those that are can reach out ten feet through the air to strike the clueless and the negligent:
Re: Grenadier's big thread of Röntgen related shenanigans
klugesmith, Mon Aug 08 2011, 11:08PM
The cylinder in picture weighed about a pound more than the other one from same vendor, and sloshed when tilted.
Yes, SF6 is about as potent a greenhouse gas as anything, when its atmospheric lifetime is figured in. A commonly cited value is 24000 times more than same weight of CO2. By that reckoning, global releases of SF6 (about 5e3 tons/year) will cause about 1/250 as much anthropogenic global warming as our 30e9 tons of CO2. They haven't found a substitute, so mitigation efforts (as with freons today) are aimed at reducing accidental and deliberate venting.
klugesmith, Mon Aug 08 2011, 11:08PM
Xray wrote ...
I don't know how difficult or practical it would be to get SF6 gas for hobbyist use, but it would be an interesting project if someone were to make an X-ray head that was insulated with SF6! I know that SF6 is a very dense "greenhouse gas", so there may be very strict EPA rules and regulations that apply to its sale, storage, and use. Electrical power distribution companies use it in many of their hv circuit breakers and other hv components, but I believe that it's being phased out because of its negative impact on the environment.
Keep one's eyes open at hamfests! I don't know how difficult or practical it would be to get SF6 gas for hobbyist use, but it would be an interesting project if someone were to make an X-ray head that was insulated with SF6! I know that SF6 is a very dense "greenhouse gas", so there may be very strict EPA rules and regulations that apply to its sale, storage, and use. Electrical power distribution companies use it in many of their hv circuit breakers and other hv components, but I believe that it's being phased out because of its negative impact on the environment.
The cylinder in picture weighed about a pound more than the other one from same vendor, and sloshed when tilted.
Yes, SF6 is about as potent a greenhouse gas as anything, when its atmospheric lifetime is figured in.
A commonly cited value is 24000 times more than same weight of CO2. By that reckoning, global releases of SF6 (about 5e3 tons/year) will cause about 1/250 as much anthropogenic global warming as our 30e9 tons of CO2. They haven't found a substitute, so mitigation efforts (as with freons today) are aimed at reducing accidental and deliberate venting.Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Tue Aug 09 2011, 02:51AM
Heh... happens with my CW in this thing. That is the reason I'm setting the heater to a fixed voltage, so the only adjustments would be exposure time and kVp. Current doesn't [didn't] seem to vary that much when I changed the voltage, maybe a difference of 300uA between 70kV and 45kV.
I've installed the CEI tube in the head, just need to wait for some parts in the mail now to fix the microelectronics. Got _lots_ of 5V and 18V TVS diodes.
Adam Munich, Tue Aug 09 2011, 02:51AM
Proud Mary wrote ...
I'm sure a good many hastily assembled X-ray experiments dissapoint because too much attention has been paid to ever higher voltage, without thought to the consequences of high PSU output impedance, with the result that the anode voltage falls flat on its face as soon as the tube starts to draw current.
I'm sure a good many hastily assembled X-ray experiments dissapoint because too much attention has been paid to ever higher voltage, without thought to the consequences of high PSU output impedance, with the result that the anode voltage falls flat on its face as soon as the tube starts to draw current.
Heh... happens with my CW in this thing. That is the reason I'm setting the heater to a fixed voltage, so the only adjustments would be exposure time and kVp. Current doesn't [didn't] seem to vary that much when I changed the voltage, maybe a difference of 300uA between 70kV and 45kV.
I've installed the CEI tube in the head, just need to wait for some parts in the mail now to fix the microelectronics. Got _lots_ of 5V and 18V TVS diodes.
Re: Grenadier's big thread of Röntgen related shenanigans
Proud Mary, Tue Aug 09 2011, 08:05AM
The problem with this approach is that you may find the anode heat capacity exceeded on higher settings of kVp, and have no way to bring it down. At the least this will quickly wreck your focal spot with pitting and fissures, as well as depositing a brown haze of conductive tungsten on the inside of the glass at a higher than normal rate.
Proud Mary, Tue Aug 09 2011, 08:05AM
Grenadier wrote ...
Heh... happens with my CW in this thing. That is the reason I'm setting the heater to a fixed voltage, so the only adjustments would be exposure time and kVp. Current doesn't [didn't] seem to vary that much when I changed the voltage, maybe a difference of 300uA between 70kV and 45kV.
Proud Mary wrote ...
I'm sure a good many hastily assembled X-ray experiments dissapoint because too much attention has been paid to ever higher voltage, without thought to the consequences of high PSU output impedance, with the result that the anode voltage falls flat on its face as soon as the tube starts to draw current.
I'm sure a good many hastily assembled X-ray experiments dissapoint because too much attention has been paid to ever higher voltage, without thought to the consequences of high PSU output impedance, with the result that the anode voltage falls flat on its face as soon as the tube starts to draw current.
Heh... happens with my CW in this thing. That is the reason I'm setting the heater to a fixed voltage, so the only adjustments would be exposure time and kVp. Current doesn't [didn't] seem to vary that much when I changed the voltage, maybe a difference of 300uA between 70kV and 45kV.
The problem with this approach is that you may find the anode heat capacity exceeded on higher settings of kVp, and have no way to bring it down. At the least this will quickly wreck your focal spot with pitting and fissures, as well as depositing a brown haze of conductive tungsten on the inside of the glass at a higher than normal rate.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Tue Aug 09 2011, 02:45PM
Hrm true. According to the charts at 150w the anode will reach 6kj in 1 min. So I'll limit the max power to 115w.
But now cei has me confused. It says tp use the grid as Hv ground and connect it to the heater with "15 / 25 kohms" or the focal spot will be affected. Not sure how to go about this when Hv ground == heater ground.
< ocx 70-g.
Adam Munich, Tue Aug 09 2011, 02:45PM
Hrm true. According to the charts at 150w the anode will reach 6kj in 1 min. So I'll limit the max power to 115w.
But now cei has me confused. It says tp use the grid as Hv ground and connect it to the heater with "15 / 25 kohms" or the focal spot will be affected. Not sure how to go about this when Hv ground == heater ground.
< ocx 70-g.Re: Grenadier's big thread of Röntgen related shenanigans
klugesmith, Tue Aug 09 2011, 06:08PM
With 6 kJ the anode is going to be damn hot -- the limit is from thermal stress around the glass/metal seal.
You could easily estimate the copper mass and temperature rise.
2. Look at the connection schematic in the datasheet. If you want to use the third wire (grid/focus) as CEI intended, your battery-powered heater supply must float, with a resistor of about 20K between one side and the grid. Negative side of HV supply goes to the grid.
When there is no anode current, grid and heater are at the same potential.
At an instant when there is 10 mA of HV current, the 10 mA flows through the 20K resistor and makes the grid 200 V negative with respect to the heater. This tends to reduce (regulate) the HV current, as well as focus the spot.
klugesmith, Tue Aug 09 2011, 06:08PM
Grenadier wrote ...
Hrm true. According to the charts at 150w the anode will reach 6kj in 1 min. So I'll limit the max power to 115w.
But now cei has me confused. It says tp use the grid as Hv ground and connect it to the heater with "15 / 25 kohms" or the focal spot will be affected. Not sure how to go about this when Hv ground == heater ground.
< ocx 70-g.
1. What are the cooling conditions (e.g. natural convection in oil?) for which the heat capacity chart applies?Hrm true. According to the charts at 150w the anode will reach 6kj in 1 min. So I'll limit the max power to 115w.
But now cei has me confused. It says tp use the grid as Hv ground and connect it to the heater with "15 / 25 kohms" or the focal spot will be affected. Not sure how to go about this when Hv ground == heater ground.
< ocx 70-g.With 6 kJ the anode is going to be damn hot -- the limit is from thermal stress around the glass/metal seal.
You could easily estimate the copper mass and temperature rise.
2. Look at the connection schematic in the datasheet. If you want to use the third wire (grid/focus) as CEI intended, your battery-powered heater supply must float, with a resistor of about 20K between one side and the grid. Negative side of HV supply goes to the grid.
When there is no anode current, grid and heater are at the same potential.
At an instant when there is 10 mA of HV current, the 10 mA flows through the 20K resistor and makes the grid 200 V negative with respect to the heater. This tends to reduce (regulate) the HV current, as well as focus the spot.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Tue Aug 09 2011, 06:17PM
Problem is, the heater supply doesn't float, it's grounded. The Hv supply sends +75kV to the anode at full blast, while the other end is attached to the same ground (via a 3mA meter).
The problem I have is, I can't float ground 200V below ground!
Adam Munich, Tue Aug 09 2011, 06:17PM
Problem is, the heater supply doesn't float, it's grounded. The Hv supply sends +75kV to the anode at full blast, while the other end is attached to the same ground (via a 3mA meter).
The problem I have is, I can't float ground 200V below ground!
Re: Grenadier's big thread of Röntgen related shenanigans
Xray, Tue Aug 09 2011, 06:48PM
You are absolutely correct. When a "grid type" of X-ray tube is used in an AC (60Hz) tube head, the grid (which is really the focusing cup) is tied to the "hot" lead of a 35KV winding, and the filament is heated with a low voltage winding on the hv transformer. The other 35KV winding is tied to the anode (in opposite phase), and so the tube effectively "sees" 70KV across it. The filament supply has to be very well insulated because that low filament voltage sits "floating" at 35KV above ground! When the tube draws current, the voltage drop across the grid resistor is what gives the tube the proper bias which not only controls the tube current, but it sets the proper voltage on the focusing cup that will create a very small focal spot on the anode target. The focusing cup acts like an electric "lens". In an ideal world, you want the focal spot to be very tiny so that it produces a "point source" of X-ray photons. But in reality, it's always a tradeoff between focal spot size (which determines image resolution) and the amount of power that the tube can handle (which determines image intensity and contrast).
In a DC (also called high frequency) tube head, the filament is at ground potential, and usually fed from a regulated DC power supply. The grid voltage is controlled with circuitry that not only sets the proper operating bias on the tube, but it is sometimes used to turn the tube on and off for precise exposure timing, and it provides much steeper rise and fall times than you can get by turning the hv power on and off, which is the usual method of timing the exposures.
Xray, Tue Aug 09 2011, 06:48PM
Klugesmith wrote ...
2. Look at the connection schematic in the datasheet. If you want to use the third wire (grid/focus) as CEI intended, your battery-powered heater supply must float, with a resistor of about 20K between one side and the grid. Negative side of HV supply goes to the grid.
When there is no anode current, grid and heater are at the same potential.
At an instant when there is 10 mA of HV current, the 10 mA flows through the 20K resistor and makes the grid 200 V negative with respect to the heater. This tends to reduce (regulate) the HV current, as well as focus the spot.
2. Look at the connection schematic in the datasheet. If you want to use the third wire (grid/focus) as CEI intended, your battery-powered heater supply must float, with a resistor of about 20K between one side and the grid. Negative side of HV supply goes to the grid.
When there is no anode current, grid and heater are at the same potential.
At an instant when there is 10 mA of HV current, the 10 mA flows through the 20K resistor and makes the grid 200 V negative with respect to the heater. This tends to reduce (regulate) the HV current, as well as focus the spot.
You are absolutely correct. When a "grid type" of X-ray tube is used in an AC (60Hz) tube head, the grid (which is really the focusing cup) is tied to the "hot" lead of a 35KV winding, and the filament is heated with a low voltage winding on the hv transformer. The other 35KV winding is tied to the anode (in opposite phase), and so the tube effectively "sees" 70KV across it. The filament supply has to be very well insulated because that low filament voltage sits "floating" at 35KV above ground! When the tube draws current, the voltage drop across the grid resistor is what gives the tube the proper bias which not only controls the tube current, but it sets the proper voltage on the focusing cup that will create a very small focal spot on the anode target. The focusing cup acts like an electric "lens". In an ideal world, you want the focal spot to be very tiny so that it produces a "point source" of X-ray photons. But in reality, it's always a tradeoff between focal spot size (which determines image resolution) and the amount of power that the tube can handle (which determines image intensity and contrast).
In a DC (also called high frequency) tube head, the filament is at ground potential, and usually fed from a regulated DC power supply. The grid voltage is controlled with circuitry that not only sets the proper operating bias on the tube, but it is sometimes used to turn the tube on and off for precise exposure timing, and it provides much steeper rise and fall times than you can get by turning the hv power on and off, which is the usual method of timing the exposures.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Tue Aug 09 2011, 07:07PM
Well I'm just trying to get a small focal spot, and the current will be set via the fixed heater voltage. This machine is designed for long exposures at low luminance, so precise control over the exposure duration is not needed.
If this tube requires the grid to be biased at a certain voltage then I'll have to pick a different tube since I have no way to bias the grid. All my tubes small enough to fit in here have some sort of grid, save for one which I have no data on. It has a focusing cup though, so I think I'll use the unmarked tube instead of the CEI one, even if it's anode spot is pitted.
Pitted anode spot > large unfocused spot.
Adam Munich, Tue Aug 09 2011, 07:07PM
Well I'm just trying to get a small focal spot, and the current will be set via the fixed heater voltage. This machine is designed for long exposures at low luminance, so precise control over the exposure duration is not needed.
If this tube requires the grid to be biased at a certain voltage then I'll have to pick a different tube since I have no way to bias the grid. All my tubes small enough to fit in here have some sort of grid, save for one which I have no data on. It has a focusing cup though, so I think I'll use the unmarked tube instead of the CEI one, even if it's anode spot is pitted.
Pitted anode spot > large unfocused spot.
Re: Grenadier's big thread of Röntgen related shenanigans
Proud Mary, Tue Aug 09 2011, 09:03PM
If you're planning to stick with the hobby for some time, it's worthwhile building an independent grid bias supply, which need not be complex or costly, because very little power is required.
As an alternative, you could wire 22 9V PP3s in series to get your 200V. So little current is drawn that the batteries will last for years. You also have the option of easy sign reversal if you get into grounded anode mode, where many of the Be window tubes are at.
Proud Mary, Tue Aug 09 2011, 09:03PM
Grenadier wrote ...
Well I'm just trying to get a small focal spot, and the current will be set via the fixed heater voltage. This machine is designed for long exposures at low luminance, so precise control over the exposure duration is not needed.
If this tube requires the grid to be biased at a certain voltage then I'll have to pick a different tube since I have no way to bias the grid. All my tubes small enough to fit in here have some sort of grid, save for one which I have no data on. It has a focusing cup though, so I think I'll use the unmarked tube instead of the CEI one, even if it's anode spot is pitted.
Pitted anode spot > large unfocused spot.
Well I'm just trying to get a small focal spot, and the current will be set via the fixed heater voltage. This machine is designed for long exposures at low luminance, so precise control over the exposure duration is not needed.
If this tube requires the grid to be biased at a certain voltage then I'll have to pick a different tube since I have no way to bias the grid. All my tubes small enough to fit in here have some sort of grid, save for one which I have no data on. It has a focusing cup though, so I think I'll use the unmarked tube instead of the CEI one, even if it's anode spot is pitted.
Pitted anode spot > large unfocused spot.
If you're planning to stick with the hobby for some time, it's worthwhile building an independent grid bias supply, which need not be complex or costly, because very little power is required.
As an alternative, you could wire 22 9V PP3s in series to get your 200V. So little current is drawn that the batteries will last for years. You also have the option of easy sign reversal if you get into grounded anode mode, where many of the Be window tubes are at.
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Tue Aug 09 2011, 10:44PM
True. Well this machine will be a "self contained unit", so not much will be adjustable. In the future I plan on making an "x-ray tube test rig".
Adam Munich, Tue Aug 09 2011, 10:44PM
True. Well this machine will be a "self contained unit", so not much will be adjustable. In the future I plan on making an "x-ray tube test rig".
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Thu Sept 22 2011, 01:29AM
SOOO... I got it running agian. Worked fine at 100W, and for a while at 200W.
But then, it stopped radiating. Nothing exploded this time; just stopped making rays. Powered it up a few times after that and read 15kV on the kVmeter, 1.5mA on the other one. I decreased the heater voltage and mA decreased, so I assume that the tube is still working as it should. However, voltage didn't increase anything special so I thought the CW took a shit.
After tearing apart the head and getting oily again, I come to find out that both the CW ant tube were OK. Turns out the FBT died on me, internal arcing on the LV windings.
Upon testing the ZVS with another FBT to make sure that was not the issue, I managed to make it the issue by accidentally shorting a primary coil and burning out the volt regulator. Plan on fixing that soon.
Back to the failed FBT. I checked the secondary and it was intact, 470 ohms. That means it WAS the LV windings that failed, and lacking anything else to do I ripped 'em out.
I'm also replacing the core, since the other one was a bit too puny for 200W. This one might work...
Adam Munich, Thu Sept 22 2011, 01:29AM
SOOO... I got it running agian. Worked fine at 100W, and for a while at 200W.
But then, it stopped radiating. Nothing exploded this time; just stopped making rays. Powered it up a few times after that and read 15kV on the kVmeter, 1.5mA on the other one. I decreased the heater voltage and mA decreased, so I assume that the tube is still working as it should. However, voltage didn't increase anything special so I thought the CW took a shit.
After tearing apart the head and getting oily again, I come to find out that both the CW ant tube were OK. Turns out the FBT died on me, internal arcing on the LV windings.
Upon testing the ZVS with another FBT to make sure that was not the issue, I managed to make it the issue by accidentally shorting a primary coil and burning out the volt regulator. Plan on fixing that soon.
Back to the failed FBT. I checked the secondary and it was intact, 470 ohms. That means it WAS the LV windings that failed, and lacking anything else to do I ripped 'em out.
I'm also replacing the core, since the other one was a bit too puny for 200W. This one might work...
Re: Grenadier's big thread of Röntgen related shenanigans
Adam Munich, Thu Jan 05 2012, 05:04AM
It is done.
Adam Munich, Thu Jan 05 2012, 05:04AM
It is done.
Re: Grenadier's big thread of Röntgen related shenanigans
Xray, Thu Jan 05 2012, 05:42AM
Way ta go, Grenadier! GOOD JOB on a rather complex project. You got my vote on BuildLounge. Now if every other 4hv member would vote for you, then you'd have a good chance of winning that laser cutter! Good Luck!
Xray, Thu Jan 05 2012, 05:42AM
Way ta go, Grenadier! GOOD JOB on a rather complex project. You got my vote on BuildLounge. Now if every other 4hv member would vote for you, then you'd have a good chance of winning that laser cutter! Good Luck!
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