Making a Geiger-Müller Counter

uzzors2k, Sun Jul 22 2007, 12:47PM

I plan on making a Geiger counter so I can sense x-ray leakage from my future x-ray setup. I have a few questions about the tubes though. I've sighted out two different tubes, the STS5 and the FHZ74V. I've found very little information on them besides pictures. First of all which would be best suited for detecting x-rays/gamma rays? I assume both will work, but it seems that some tubes are made for alpha and others for beta radiation. Shouldn't x-rays be capable of exciting any tube?

Info on the FHZ74V.



I found nothing on the STS5, besides a picture from the seller's webshop.

1185107856 95 FT0 Sts5
Re: Making a Geiger-Müller Counter
Sulaiman, Sun Jul 22 2007, 01:59PM

The tube in bottom photo looks like the SBM-20 in my russian GM counter
perfect for x-rays.

Is it worth making a GM counter when they're so cheap on eBay?
Re: Making a Geiger-Müller Counter
c4r0, Sun Jul 22 2007, 03:09PM

Yes, it's SBM-20 or similar on the second photo and it's good for x-rays detecting. You just need about 400VDC to power it. Number of pulses in 40s measure time is equal to radiation "power" in uR/h (1uR/h = 0.01uSv/h). You sholud get about 15 pulses (in 40s time) from natural background radiation. If you want I can send you schematics of a few russian geiger counters using this tube smile
Re: Making a Geiger-Müller Counter
uzzors2k, Sun Jul 22 2007, 03:35PM

That would be great c4r0. cheesey

I can't find any cheap Geiger counters on ebay atm, and I can buy the GM tube from the same place as the HV rectifiers which I'll use for x-ray tubes. What I save in shipping costs will make up for it.
Re: Making a Geiger-Müller Counter
c4r0, Sun Jul 22 2007, 04:01PM

Ok, so this is the simplest and the most useful one - russian dosimeter BELLA:
1185119616 151 FT28803 Bella


It simply counts the pulses and displays it. Uses one SBM-20 tube

This one is more complicated - also russian POLARON-PRIPYAT: 1185119616 151 FT28803 Pripyat2


Uses two SBM-20 tubes.

And here is an old (1960s) Polish Army radiometer DP-66: 1185119616 151 FT28803 Dp66


It has three diferent tubes becouse of wide measure range (0,5mR/h - 200R/h), one of the tubes is SBM-20.

Also these websites should help you:
Link2
Link2
Re: Making a Geiger-Müller Counter
Sulaiman, Sun Jul 22 2007, 04:30PM

Tube specifications
]1185121847_162_FT28803_sbm20.pdf[/file]
Re: Making a Geiger-Müller Counter
uzzors2k, Sun Jul 22 2007, 05:13PM

Wow, thanks guys. I'll order a SBM-20 then, and tell how the counter turns out.
Re: Making a Geiger-Müller Counter
Simon, Mon Jul 23 2007, 12:34AM

Uzzors wrote ...

Shouldn't x-rays be capable of exciting any tube?

GM tubes are often not so sensitive to gamma and X rays but it should work.
Re: Making a Geiger-Müller Counter
uzzors2k, Fri Aug 17 2007, 07:50PM

Well, he was all out of SBM-20s so I had to buy a FHZ74. I put together a simple circuit which provides a regulated output, and pops a speaker when the output is grounded (tube ionization). This gives the cool crackling sound familiar from games and movies.

1187377776 95 FT28803 Geiger Counter Schematic


Anyway, it's not acting like I expected it to, which is somewhere around 15 pops per 40 seconds.With the tube voltage set to 575V I get constant crackling, as though I were in the middle of Chernobyl. If I set the tube voltage down to 420V the crackling stops altogether. I don't even get occasional pops from background radiation. Is this normal behavior? I haven't tried the counter near a known radioactive source yet, maybe the counting starts again or increases even more. I'm not sure what the different voltages in the datasheet are for, but "arbeitsspannung" (working-voltage) must be what I need to drive the tube at. Will the tube only function properly at the working voltage, close to 500V? Or is the excessive crackling due to the circuit design?

]FHZ74.pdf[/file]
Re: Making a Geiger-Müller Counter
Sulaiman, Fri Aug 17 2007, 09:21PM

I'm not sure but I think that your GM tube is for high radiation environments
50 r/hr is high (500 r over 5 hours is lethal according to wikipedia)
and I think the spec. gives 0 to 5 impulses per minute for background radiation
much less than the SBM20.

The constant crackling at 525 V is due to over-voltage breakdown in the tube (bad)
420 V should be good though.

Hopefully someone can give a second opinion?
Re: Making a Geiger-Müller Counter
uzzors2k, Sat Aug 18 2007, 12:57PM

Your opinion strengthens my suspicion, Suliaman. I set the tube voltage to 420 and listened for 2 minutes, and I heard a total of 3 pops. About right I guess. The lack of sensitivity bothers me though, if it's made for high radiation environments will the x-rays still excite the tube? And to think I could have bought a 1r/hr tube instead... Not that I will be relying on the counter for protection, everything will be encased in lead/steel shielding, but it would be nice to know if x-rays are even being generated.
Re: Making a Geiger-Müller Counter
EEYORE, Sat Aug 18 2007, 04:44PM

Uzzors wrote ...

Your opinion strengthens my suspicion, Suliaman. I set the tube voltage to 420 and listened for 2 minutes, and I heard a total of 3 pops. About right I guess. The lack of sensitivity bothers me though, if it's made for high radiation environments will the x-rays still excite the tube? And to think I could have bought a 1r/hr tube instead... Not that I will be relying on the counter for protection, everything will be encased in lead/steel shielding, but it would be nice to know if x-rays are even being generated.


You need to find a GM tube with MUCH more sensitivity for xrays. 1r/hr is still way too high. Get a CDV700 off of ebay. It will go to 50mR/Hr. Chest xrays are like 10mR...
Matt
Re: Making a Geiger-Müller Counter
uzzors2k, Sat Aug 18 2007, 07:22PM

So much for that then, at least I'll know where to find safe shelter when WW3 breaks out. tongue If I really need the GM-counter for the x-ray machine I'll buy a more sensitive tube. I've found SBM-20 tubes on ebay for 17 USD, their range is 40 - 400 mR/hr, which should suffice. Thanks for the help everyone.
Re: Making a Geiger-Müller Counter
Sulaiman, Sat Aug 18 2007, 08:44PM

Just for reference,
I live in a VERY low background radiation area
and my SBM20 gives about one click every three seconds average.
Re: Making a Geiger-Müller Counter
c4r0, Sat Aug 25 2007, 11:32AM

Uzzors wrote ...
If I really need the GM-counter for the x-ray machine I'll buy a more sensitive tube. I've found SBM-20 tubes on ebay for 17 USD, their range is 40 - 400 mR/hr, which should suffice.
Remember that radiation from x-ray tube can easily overload this GM tube. Then it becomes sth like short-circuit and the counter stops, just like there was no radiation!
Re: Making a Geiger-Müller Counter
uzzors2k, Sun Aug 26 2007, 12:51PM

Really? Maybe the purchase wasn't so bad after all. Was this with your medical x-ray tube, the common vacuum tube on the SSTC, or both?
Re: Making a Geiger-Müller Counter
c4r0, Mon Aug 27 2007, 02:25PM

Only with medical x-ray tube. It can produce even 100R/h easily :)

Link2
Re: Making a Geiger-Müller Counter
sparky, Mon Aug 27 2007, 09:21PM

I know of several US based dealers who sell reconditioned -remade civil defense counters. Sure you could build one, but for $100 USD you can get one that is all remade. My brother owns a CDV-700 that has been altered to 100mr/hr and has a pancake probe that does alpha-beta-gamma and XRAYS. Also it comes with a scintillator kit and a digital CPM meter built in :) all for $200. You can't beat that kind of pricing.
Re: Making a Geiger-Müller Counter
uzzors2k, Sat Dec 08 2007, 09:48PM

I finished my mini Geiger counter last weekend, but without any known radiative sources it's hard to test. The circuit works anyway, so I'll see how the tube works when I build my x-ray machine. (if it works) I bought a small SBM 21 which has a range of 40 to 400 mRh, so if there are any x-rays present it should sense them. A buzzer and an ultra bright LED are activated when the GM tube is ionized.

1197150081 95 FT28803 Boxed Up 1197150081 95 FT28803 Inside View


In the end it would have been cheaper just to just buy a finished Geiger counter like Sulaiman did.
Re: Making a Geiger-Müller Counter
EEYORE, Mon Dec 10 2007, 04:11AM

Neat, but yes you can get nice calibrated cdv700's for ~$45.00 on ebay...
40mR is alot.
Matt
Re: Making a Geiger-Müller Counter
Dr. Who, Sat Dec 15 2007, 12:38AM

A household smoke alarm is the most commonly available radioactive source - many use a sensor containing an alpha emitter.
Re: Making a Geiger-Müller Counter
plazmatron, Sun Dec 16 2007, 10:04PM

Yep, Am-241 from smoke alarms (though you have to place it close to the tube to get a good reading), Th-232 from the older gas mantles, an theres always e-bay, some sellers occasionally sell old surplus luminous watch hands, containing Radium ( I managed to buy about 50 in one go!)

As c4r0 says, x-rays, will easily overload geiger counters, since they produce millions of x-ray photons/sec, so you may be as well getting an ionisation chamber detector, like the Radiac`s on e-bay, for high dose rates. Of course, because of their sensitivity, geiger counters, are great for checking the integrity of your shielding.

Leslie
Re: Making a Geiger-Müller Counter
MOT_man, Mon Dec 17 2007, 03:16PM

Red/ Yellow Fiestaware from 1960's and below are colored with Uranium/ Thorium based glazes - Vasoline glass (neon tinge to it) glows under UV light contains Uranium Nitrate. Both types can be strongly radioactive, but nowhere near hazardous.... I still use them to serve off of... :) They are sealed so contamination risk is nil.
Re: Making a Geiger-Müller Counter
Proud Mary, Thu Jan 17 2008, 06:54PM

General purpose beta/gamma GM tubes are not a good way to detect and measure X-rays, and some will not react at all to even high levels of hazardous low-energy X-rays. There are specially produced X-ray sensitive GM tubes which have a much higher gas pressure, have a mica end window like a longer version of an alpha tube. Cold War era GM tubes were usually designed to be very insensitive so as to have greater linearity at high count rates of hard radiation.

Tubes with metal jackets, or where the cathode forms the tube case, will block almost all of the low energy X-rays likely to be produced by a small scale experimental set up, and so detect little or nothing. Think of the thin aluminium filters used to block low energy X-rays in dental machines. And remember that low energy X-rays are the most hazardous of all!

An ionization chamber is almost always to be preferred for the measurement of X-rays since chamber current is proportional to X-ray dose rate. One can be readily built around a diecast metal box and can be operated at atmospheric pressure so as to have only the thinnest polythene window - or no window at all. One of the plates should be charged, and the other taken to a guarded ultra high impedance amplifier which forms the first stage of a pico-ammeter. And away you go!
Re: Making a Geiger-Müller Counter
c4r0, Thu Jan 17 2008, 09:27PM

My counters based on SBM-20 g-m tube easily detects x-rays generated by x-ray tube powered from 50kV. I'm sure that measurement is much lower than it should be, however it detects this radiation. SBM-20 is designed for measuring radiation >100keV.

Medical x-ray machines usually uses 1-2mm Alluminium for filtering, but it's not so necessary until you're not going to x-ray yourself :)
Re: Making a Geiger-Müller Counter
plazmatron, Mon Jan 28 2008, 12:46AM

I have a cd-v700 geiger counter and even my smallest (12W, 40kV) tube will peg the meter on the highest scale! (with Beta shield open)

I also have one of those Russian counters that uses one of those horrible mini steel can geiger tubes, the SBM21, and again, my x-ray sources will easily drive it to saturation.

The problem with these is accuracy of the reading. Normally you would use an ionization detector, or a dosimeter, from which you would be able to calculate your dose rate. However even a relatively insensitive tube, like the SBM21 should be able to verify the presence of radiation between 30 and 100keV (just assume the reading to be much higher than it is, and take precautions accordingly. Remember, you are aiming for NO detectable radiation, in the area you are in)

Leslie
Re: Making a Geiger-Müller Counter
Proud Mary, Sat Feb 02 2008, 03:28PM

I believe that mica end-window GM-tubes - like those found in the legendary Mullard ZP1400 series - can generally detect X-rays down to about 10keV along the length of the tube's major axis, where the rays must pass through the maximum amount of gas. Even so, counting efficiency will be very low, with few X-ray photons being able to create sufficient ion pairs to start a Townsend avalanche.

The energy response curve of typical GM tubes is such that a peak in sensitivity spread across 10 - 100keV results in significant over-counting of low energy X-rays - as much as 500% for an uncompensated tube when compared with a standard 137-Cs 662 keV calibration standard.
Re: Making a Geiger-Müller Counter
plazmatron, Thu Feb 07 2008, 12:59PM

Harry wrote ...


The energy response curve of typical GM tubes is such that a peak in sensitivity spread across 10 - 100keV results in significant over-counting of low energy X-rays - as much as 500% for an uncompensated tube when compared with a standard 137-Cs 662 keV calibration standard.


That would explain the frighteningly high readings of the CD V700 when compared with a proper dosimeter ! ( I have several, and they all agree with each other).
Re: Making a Geiger-Müller Counter
Proud Mary, Thu Feb 07 2008, 04:36PM

Leslie, here is a fairly typical Photon Energy Response Curve for a small uncompensated G-M tube normalized to unity at 662 keV with beam perpendicular to detector wall.

Link2

When you are operating around the low-energy response peak then a relatively small increase - or decrease - of photon energy [X-ray tube anode voltage] can cause a very large apparent count rate change. Also, it is as well to remember that a typical GM tube may show roughly the same count rate for 20keV photons as for 120keV on the other side of the peak - an ambiguous state of affairs that can easily mislead.
Re: Making a Geiger-Müller Counter
Conundrum, Fri Feb 08 2008, 09:46PM

Hmm. MacGyver would be impressed :)

I still want to know why someone hasn't devised a servo-like arrangement that simply moves a variable thickness lead/copper alloy on a pivot across the sensor. As the radiation flux increases it rotates to keep the sensor from saturating then applies a scaling factor.

/me scuttles off to try this.

-A

Re: Making a Geiger-Müller Counter
uzzors2k, Sat Feb 09 2008, 01:42PM

Leslie kindly donated some radium watch hands so I could test my counter. The count rate at different distances corresponds to what Leslie got with his SBM-21 counter, so my homemade version definitely works!

226 Watch Hands
Re: Making a Geiger-Müller Counter
Proud Mary, Sat Feb 09 2008, 02:21PM

Uzzors wrote ...

Leslie kindly donated some radium watch hands so I could test my counter. The count rate at different distances corresponds to what Leslie got with his SBM-21 counter, so my homemade version definitely works!

226 Watch Hands


There are plenty of thorium and uranium minerals to look for in Norway!
Re: Making a Geiger-Müller Counter
uzzors2k, Sat Feb 09 2008, 05:31PM

Good call, I had forgotten about that. Next time I'm out hiking I'll bring the counter with me and see if I find anything.
Re: Making a Geiger-Müller Counter
plazmatron, Sun Feb 10 2008, 07:03PM

Good Idea!
I went up to Tyndrum mine in Scotland yeaterday, to prospect for Uranium, with my CD-V700. I didnt get lucky, I`m afraid, but the background count up there is impessively high! I`m thinking Cornwall next, since the Uraninite deposits at Tyndrum are very minor, but it will be a thousand mile round trip! sad
Re: Making a Geiger-Müller Counter
Proud Mary, Sun Feb 10 2008, 08:01PM

plazmatron wrote ...

Good Idea!
I went up to Tyndrum mine in Scotland yeaterday, to prospect for Uranium, with my CD-V700. I didnt get lucky, I`m afraid, but the background count up there is impessively high! I`m thinking Cornwall next, since the Uraninite deposits at Tyndrum are very minor, but it will be a thousand mile round trip! sad

I visited the spoil heaps of several ruined Cornish tin mines once noted for their pitchblende, without discovering anything very interesting, but the beach near St Austell produced some remarkable treasures in just a few minutes.

The main part of the beach is covered with sand, but at the back of the beach a natural bank of pebbles has formed. In this I found water-worn pitchblende pebbles so active that I could detect them at two or three metres. The most active of these conspicuously heavy, chocolate-brown pebbles measured 150uSv/hr @ 10cm, and the least active, which was a much lighter brown, about 20uSv/hr.

I talked to local folk [who knew nothing of the pitchblende] and it seems that at times of winter storms and tides, the sand may be swept from the beach altogether, exposing the country rock beneath. Here I would expect to find a wealth of pitchblende, as such dense but smooth pebbles would naturally find their way to the bottom layer immediately above the bed rock, and be last to be swept away. [ i.e. gravimetric separation]

These rich ores perhaps come from the same load worked on by the long defunct British and General Radium Corporation Ltd mine at South Terras, which lay between St. Stephen and the Grampound Road somewhat inland from St Austell.

Link2

You can see on the Google Maps Satellite image the uranium mill chimney sticking up out of the trees of a small wood which has now overgrown the whole site.

I also found this which may interest Leslie:

"In Scotland the most important uranium mineralization occurs in three locations:-

1. in low-grade, phosphatic and carbonaceous horizons in the Middle Devonian lacustrine basin of the Orkneys and Caithness;

2. in Devonian arkosic breccias marginal to the Caledonian Helmsdale granite at Ousdale on the east coast of Caithness;

3. in veins marginal to the Caledonian Criffel granodiorite at Dalbeattie.

The Ousdale area was drilled in the early 1970s on a 130 m square grid with 41 percussion holes to depths of 80 m. The maximum value found was 850 ppm U within a 15 m intersection.

Uranium-lead mineralization occurs in a fault breccia in Devonian sediments at Mill of Cairston, near Stromness on Orkney. The fault was drilled by the BGS and a mining company consortium in 1971–1972 when maximum values of 1000 ppm U were found, together with 5.5% lead."

[Source: British Geological Survey, Mineral Profile, Uranium, March 2007]
Re: Making a Geiger-Müller Counter
plazmatron, Wed Feb 13 2008, 03:51AM

Thanks! I just got the pdf!
Dalbeattie looks parkticularly promising, and is only 200 miles away or so. There is a reference to Pitchblende veins being found in the cliffs there.

Leslie
Re: Making a Geiger-Müller Counter
Proud Mary, Wed Feb 13 2008, 10:26AM

There's always a good chance of finding fallen material at the foot of a cliff - if you can get to it, and it isn't under water at low tide.

Re: Making a Geiger-Müller Counter
Conundrum, Wed Feb 13 2008, 10:29AM

Conundrum wrote ...

Hmm. MacGyver would be impressed :)

I still want to know why someone hasn't devised a servo-like arrangement that simply moves a variable thickness lead/copper alloy on a pivot across the sensor. As the radiation flux increases it rotates to keep the sensor from saturating then applies a scaling factor.

/me scuttles off to try this.

EDIT:- I have three SBM 20's. One removed from my counter erroneously, the other two are in my counter. Does anyone have a use for these?

i also have some 180V zeners here that might be useful for regulating the supply.

-A


Re: Making a Geiger-Müller Counter
Proud Mary, Wed Feb 13 2008, 12:05PM

There is a detailed account of the rich uranium mineralization in the cliff top near Needle's Eye, Colvend, Dalbeattie, in MINERALOGICAL MAGAZINE, JUNE 1990, VOL. 54, PP. 129--131.
Link2
Re: Making a Geiger-Müller Counter
plazmatron, Wed Feb 13 2008, 09:28PM

Wow! that site is looking more and more delicious! Thanks Harry!
I`m thinking of taking a wee field trip!
According to auto route, I can make it there in about 3 hours, so If I set off early enough it can be a day out! cheesey
I have been dying to have a crack at extracting Uranium for some time!
Re: Making a Geiger-Müller Counter
Proud Mary, Thu Feb 14 2008, 10:26PM

plazmatron wrote ...

Wow! that site is looking more and more delicious! Thanks Harry!
I`m thinking of taking a wee field trip!
According to auto route, I can make it there in about 3 hours, so If I set off early enough it can be a day out! cheesey

There looks to be a golf course immediately behind the cliff, Leslie, perhaps right on top of the original Location 3 trench. As a fallback, you might think about getting a tide-table for the Solway Firth, and seeing how far you can get towards Needle's Eye from Sandyhills Bay at low tide. The Solway Firth is generally <5m so I'd guess you might get all the way to the foot of the cliff - immediately below the vein - at low tide, and come back with rich pickings, provided you bear in mind the great rapidity with which the tide comes in in such shallow seas, and keep a scrupulous eye on the clock when you are there!
Re: Making a Geiger-Müller Counter
plazmatron, Fri Feb 15 2008, 12:32AM

Funny you should mention that! I was just checking tides, and trying to pinpoint the exact location today.
The pair of veins are on the Southwick coastal reserve, near the Needles eye rock formation so it should be easy to spot!
The tide is fully out around 16:30 on Monday (the day I plan to go) , so I will spend the morning surveying the trench If I can find it (shouldnt be too difficult I`m cheating and using GPS!)

Thanks for the heads up on that one!
Re: Making a Geiger-Müller Counter
plazmatron, Tue Feb 19 2008, 08:26PM

Well I had a good run to the cliffs at Solway Firth on Monday, and after 5 hours or so, found some classic examples of Pitchblende!
Some are extraordinarily active, even more so than my entire radium watch hands collection!
Thanks again for the tip Harry!


Something

1203452763 1134 FT28803 Pitchblende

1203452763 1134 FT28803 Measuring
Re: Making a Geiger-Müller Counter
Proud Mary, Tue Feb 19 2008, 09:39PM

I'm really pleased for you, Leslie! I can well remember when I found some really active pieces of pitchblende at St Austell, and I could hardly believe how energetic they were.

Now you're in position to try some gamma radiography and all manner of interesting experiments. Whoo-hooo!
Re: Making a Geiger-Müller Counter
plazmatron, Thu Feb 21 2008, 07:59PM

Absolutely!
I have extracted a small quantity (2g) of fairly pure Uraninite from a soil sample, and sintered it into a small hard pellet to give autoradiography a try. The pellet measures just over 12,000 CPM (combined beta/gamma), so it should give fair results in a comparatively short space of time.

Leslie
Re: Making a Geiger-Müller Counter
Proud Mary, Thu Feb 21 2008, 10:15PM

Leslie, here's the website of a very inventive chap whose work I think you'll like if you don't already know of it:

Link2
Re: Making a Geiger-Müller Counter
plazmatron, Tue Feb 26 2008, 01:53AM

Yes I`ve seen his page before. He has done some incredible work. Which reminds me, I must get a decent vacuum setup, I just have to try and build a x-ray tube!

Re: Making a Geiger-Müller Counter
Seoul_lasers, Thu Aug 21 2008, 05:10AM

c4r0 wrote ...

My counters based on SBM-20 g-m tube easily detects x-rays generated by x-ray tube powered from 50kV. I'm sure that measurement is much lower than it should be, however it detects this radiation. SBM-20 is designed for measuring radiation >100keV.

Medical x-ray machines usually uses 1-2mm Alluminium for filtering, but it's not so necessary until you're not going to x-ray yourself :)

Umm, they usually use lead lining around the tube for filtering. Beryllium is also sometimes used as well as it has a high atomic number. You can seriouly burn yourself with homemade X-rays. ( just like a very bad sunburn) I'd advise you BE CAREFUL.
50Kv-60Kv is more often the range for a dental x-ray machine.
To really see if you have X-rays use a ZnS (Ag) screen below the tube. it will glow green then the power has been turned on.
I have seen small radiotube X-ray machines make some impressive X-ray pictures.
Re: Making a Geiger-Müller Counter
c4r0, Thu Aug 21 2008, 09:51AM

Seoul_lasers wrote ...

c4r0 wrote ...

My counters based on SBM-20 g-m tube easily detects x-rays generated by x-ray tube powered from 50kV. I'm sure that measurement is much lower than it should be, however it detects this radiation. SBM-20 is designed for measuring radiation >100keV.

Medical x-ray machines usually uses 1-2mm Alluminium for filtering, but it's not so necessary until you're not going to x-ray yourself :)

Umm, they usually use lead lining around the tube for filtering. Beryllium is also sometimes used as well as it has a high atomic number. You can seriouly burn yourself with homemade X-rays. ( just like a very bad sunburn) I'd advise you BE CAREFUL.
50Kv-60Kv is more often the range for a dental x-ray machine.
To really see if you have X-rays use a ZnS (Ag) screen below the tube. it will glow green then the power has been turned on.
I have seen small radiotube X-ray machines make some impressive X-ray pictures.
I know that there is that lead filter, and i always unwind it off the g-m tube. By the way it's not lead actually becouse i've checked if its good for x-ray tube shielding and its not, about 0.5mm of this metal attenuates just like 2mm of Al.

You wrote that I should use an intensifying screen for detection. Well, in my case the screen glows only in the main x-ray beam so you would say that its ok and safe? My geiger counters are going mad even 5 meters behind the tube (not in front) becouse of scattered radiation and imperfect tube shielding (it can't be perfect). Also while turning anode voltage up the g-m counters laying 1m from the tube starts to tick at significantly lower voltage than the screen placed 5cm from the tube starts to glow visibly. So in my opinion geiger counter is much better for safety radiation detection. Ofcourse it's sensitivity should be checked first.
Re: Making a Geiger-Müller Counter
Proud Mary, Thu Aug 21 2008, 01:48PM

c4r0 wrote ...

I know that there is that lead filter, and i always unwind it off the g-m tube. By the way it's not lead actually becouse i've checked if its good for x-ray tube shielding and its not, about 0.5mm of this metal attenuates just like 2mm of Al.

This is probably a Tin (Sn) or tin alloy filter to smooth out the tube's very uneven energy response curve, though Cadmium (Cd) foil is sometimes wrapped around military G-M tubes to improve neutron counting efficiency.
Re: Making a Geiger-Müller Counter
Steve Conner, Thu Aug 21 2008, 02:53PM

Seoul_lasers wrote ...

You can seriouly burn yourself with homemade X-rays. ( just like a very bad sunburn) I'd advise you BE CAREFUL.

Ironically, c4r0 once scared hell out of me by posting a picture of his sunburned face here and claiming he burnt himself with X-rays.
Re: Making a Geiger-Müller Counter
Seoul_lasers, Fri Aug 22 2008, 01:34AM

c4r0 wrote ...

Seoul_lasers wrote ...

c4r0 wrote ...

My counters based on SBM-20 g-m tube easily detects x-rays generated by x-ray tube powered from 50kV. I'm sure that measurement is much lower than it should be, however it detects this radiation. SBM-20 is designed for measuring radiation >100keV.

Medical x-ray machines usually uses 1-2mm Alluminium for filtering, but it's not so necessary until you're not going to x-ray yourself :)

Umm, they usually use lead lining around the tube for filtering. Beryllium is also sometimes used as well as it has a high atomic number. You can seriouly burn yourself with homemade X-rays. ( just like a very bad sunburn) I'd advise you BE CAREFUL.
50Kv-60Kv is more often the range for a dental x-ray machine.
To really see if you have X-rays use a ZnS (Ag) screen below the tube. it will glow green then the power has been turned on.
I have seen small radiotube X-ray machines make some impressive X-ray pictures.
I know that there is that lead filter, and i always unwind it off the g-m tube. By the way it's not lead actually becouse i've checked if its good for x-ray tube shielding and its not, about 0.5mm of this metal attenuates just like 2mm of Al.

You wrote that I should use an intensifying screen for detection. Well, in my case the screen glows only in the main x-ray beam so you would say that its ok and safe? My geiger counters are going mad even 5 meters behind the tube (not in front) becouse of scattered radiation and imperfect tube shielding (it can't be perfect). Also while turning anode voltage up the g-m counters laying 1m from the tube starts to tick at significantly lower voltage than the screen placed 5cm from the tube starts to glow visibly. So in my opinion geiger counter is much better for safety radiation detection. Ofcourse it's sensitivity should be checked first.


Oh, no.. of course USE a Geiger counter for safety you must do this!! I ment to say have the screen to make sure you tube is emitting properly.
2) BE extremely careful with the metal around the tube, there were some tubes that used Be foil
and acciental exposure to it gives you Beryllium lung eventually.
IT could be Sn but most likely NOT Aluminum. -- just be careful.
In the orginal build your own xray machine document it suggested making a lead pig to house the tube in. This allowed X-rays out of a single opening. Do you have any old
fishing weights?
Re: Making a Geiger-Müller Counter
Steve Conner, Fri Aug 22 2008, 11:35AM

wrote ...
3. in veins marginal to the Caledonian Criffel granodiorite at Dalbeattie.
Does that mean the Slab Link2 is radioactive? suprised
Re: Making a Geiger-Müller Counter
plazmatron, Mon Sept 15 2008, 03:43PM

Dr. Meh wrote ...

Does that mean the Slab Link2 is radioactive? suprised

Probably! I have made several trips now to the Dalbeattie area, and the area has significantly elevated radiation levels.
Any rock outcrops in the area containing mineral veins, will almost certainly have some measurable activity, although only a few, are significant enough for collection, or extraction.
I found an outcrop of Haematite (iron ore) that contains a significant amount of Uranium mineralization.

Leslie
Re: Making a Geiger-Müller Counter
Dragon64, Mon Sept 15 2008, 11:49PM

OT but since you guys were talking about it, I throw this out.

Is there any regions close from my city Calgary/Canada that has pitchblende or other radioactive minerals?

I know that the Lake Athabasca is rich in uranium ores but its 1000km drive...
Re: Making a Geiger-Müller Counter
Seoul_lasers, Tue Sept 16 2008, 01:31AM

hydraliskdragon wrote ...

OT but since you guys were talking about it, I throw this out.

Is there any regions close from my city Calgary/Canada that has pitchblende or other radioactive minerals?

I know that the Lake Athabasca is rich in uranium ores but its 1000km drive...


You should check with Minfile project. There is an Alberta based version I think.
Having been a collector of minerals past and present I can tell you that there are indeed uranium deposits around Alberta.
Athabasca. Drumheller there is some U associated with fossilized wood. (apparently it is pretty common) and it is usually Carnotite and or Tyuyamunite. look for yellow stains on the wood. YOu should easily get a few 1000s CPM from a medium chunk of wood.

Here in BC we have at least 10-12 areas (1 on Quadra Island) that contains U or a mix of High grade U and Th.
The most active being in the clearwater area (foghorn mtn). There is quite also quite a bit in the Okanagan valley as well.


btw- Quadra island was a bit of a fluke, and no more was found . BUT I went to the site (Radium Senator) about 4 years ago and little did I discover that there is some high counts 100s of CPM in the same area. hmm. Also people have reported some serious health effects from drinking the water on the island. (Notably Cancer).
On Quadra this could be from naturally occurring Hg, As, Sb, Te or U disolved in the water from semi Alkaline conditions.
Re: Making a Geiger-Müller Counter
Conundrum, Tue Mar 27 2018, 08:01AM

Some places actually have warning signs advising people not to pick up the "hot rocks".. mostly because this is not a good idea. The problem is that fossils can be radioactive enough to affect some laptops and there are a couple of documented cases.

A while back they had a serious problem with radioactive lightning conductors, and they occasionally show up then HAZMAT gets called in to deal with the resulting mess.
Link2
Re: Making a Geiger-Müller Counter
paulj, Wed Mar 28 2018, 08:17PM

hello,

it reminds Chernobyl, to evacuate wastes from the reactors on the roof before putting the sarcophagus, the Russians had used robots, but they all broke down because of a strong radiation, the liquidators have therefore taken over every 30 seconds, 1minutes.
Re: Making a Geiger-Müller Counter
Conundrum, Wed Apr 04 2018, 06:05PM

Note, modern laptops can be badly affected by sustained radiation even at low levels. Seems that some components can be affected in the DDR2/3 chips and low density ones (ie 2GB DDR3) can be quite sensitive.
I think its due to the refresh being marginal on a lot of them, so even a few lost electrons can cause a SEU that cascades into a BSOD if it happens frequently enough on a critical process.
Re: Making a Geiger-Müller Counter
paulj, Thu Apr 05 2018, 04:10AM

what do you mean by "low level"?
Re: Making a Geiger-Müller Counter
Conundrum, Thu Apr 05 2018, 10:24AM

From the description given in the article I found involving a radioactive fossil in someone's desk, it would be in the uSv range. Certainly it only showed up on a newer counter, the older unit saw nothing.
Re: Making a Geiger-Müller Counter
paulj, Thu Apr 05 2018, 12:16PM


1522930386 59353 FT28803 Dsc03958

1522930386 59353 FT28803 Dsc03960



you think that with this kind of ore it is possible to bug a computer?

ps, my counter to saturated, the real dose is 560 μSv.
Re: Making a Geiger-Müller Counter
Proud Mary, Thu Apr 05 2018, 09:54PM

Conundrum wrote ...

From the description given in the article I found involving a radioactive fossil in someone's desk, it would be in the uSv range. Certainly it only showed up on a newer counter, the older unit saw nothing.

The highest dose rate I've ever seen from a mineral sample was just short of 100 uSv/hr gamma from a chunk of the best Cornish pitchblende. Most pitchblende samples give less than half that value.

Re: Making a Geiger-Müller Counter
paulj, Fri Apr 06 2018, 03:56AM

Hello,

(my geiger counter is not compensated on energy, so you have to rely on CPM, not on USV / H.)

my piece contains a significant amount of uranium, and comes from a mine in the Czech Republic.

there are minerals with even higher radiation levels.

example: page 5/11 by an organization that doesn't depend on the government


Translation: Sometimes very important risks
Verifying the level of gamma radiation near minerals is a useful precaution because
in some cases, the risks may be significant.
The highest level of radiation measured by CRIIRAD on minerals to date is for a piece of
Uranium ore conserved by a resident of Saint-Priest-La-Prugne in the Loire, at its flowerbeds
(see photograph below).
The contact dose rate measured in July 2002 was 1 milliSievert per hour (Hp10 dose),
5,000 times higher than the natural background noise of the place.
At the request of CRIIRAD, this sample was taken in charge by the former mining operator (COGEMA-AREVA).

link: (in French)

Link2
Re: Making a Geiger-Müller Counter
Conundrum, Fri Apr 06 2018, 08:28PM

I should probably run some more tests, for this purpose a handful of Th welding rods or some Lo-Salt would work.
If it saturates a Geiger counter then a laptop should not stand a chance.
Depends on isotope of course as lower energy may increase error rate due to higher absorption in the silicon memory chips.
Vent holes in the memory casing would increase dosage as well.

EDIT: I found the problem. Bad RAM can happen over time and yes this can make it super sensitive to radiation.
So much so in fact that I could detect my proximity by the number of soft errors in the RAM test!
Pauli effect IRL.
This can also happen to HDD cache chips as well and can sometimes lead to data loss as even a clone will fail.

PaulL Well it was strong enough to detect on my unshielded SBM20 running at about 510V at 2" away (bag of enriched 40K) and when I tried it the RAM test failed in about an hour.
At that point it got swapped out and replaced!
Re: Making a Geiger-Müller Counter
Conundrum, Fri Feb 15 2019, 05:13AM