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Registered Member #2893
Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242
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.
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 $200. If it sells, project's over. If not, then i'll finish.
Registered Member #2893
Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242
Anders M. wrote ...
What will cost you 125$?
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)
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
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.
Registered Member #33
Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971
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.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
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?
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.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Proud Mary wrote ...
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?
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.
Registered Member #33
Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971
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?
Registered Member #2893
Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242
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?
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Anders M. wrote ...
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.
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Grenadier's big thread of Röntgen related shenanigans
