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Is that a Geiger counter in your pocket (or are you just happy to see me)?

Clive Maxfield
3/24/2011 11:29 PM EDT

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jack754
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re: Is that a Geiger counter in your pocket (or are you just happy to see me)?
jack754   4/7/2011 9:08:44 AM
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I ordered a kit after Chernobyl, not because of Chernobyl but because we were looking for a house to buy and I wanted to check these out for Radon gas. So the Geiger counter had to be able to detect alfa particles. It had a counter that displayed something like 5 and a half digits. It worked for 20 years, but no longer and I'm now looking for a replacement. The tube was supposed to have a nominal output of about 10 clicks/minute. When I first put it together it was giving more than that. I looked at the waveform in a scope and it looked like individual pulses were getting split up and counted several times, so I put in a capacitor to get it to count it as just one pulse, after which the average pulse rate was around 10/min. Here in Norway you can rent equipment to measure Radon gas. So I did this and had my Geiger counter placed beside it, so I found out what constituted an average Radon environment based on the report I got back after the official measurement. I found an old child's watch of the kind that glowed in the dark. This was my alfa source for demonstrations. I have had high metabolism and was finally treated with I-131. After some weeks I was able to check that the radiation did indeed have a half-life of 8 days.

Max The Magnificent
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re: Is that a Geiger counter in your pocket (or are you just happy to see me)?
Max The Magnificent   3/31/2011 10:27:00 AM
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Good info -- I have a do-it-yourself kit on the way -- I will report back after I've build it and played with it.

Joe.Sleator
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re: Is that a Geiger counter in your pocket (or are you just happy to see me)?
Joe.Sleator   3/31/2011 9:53:24 AM
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A buddy had given me a GM tube, but it's temporarily lost after moving, so being lazy I just bought another from Vernier. Since the information is quantum, it either clicks or it doesn't. What caused it to click is a bit more complicated. It has a mica window, so if you poke an alpha-source right up to the window it will measure that OK, but alphas don't really go through air very far, they can be blocked by paper. Betas and gammas will go further, so if you put a few mm of aluminium on the back of your instrument and point the back at your source and it still clicks, it was most likely gamma. Uncovered lying in my living room the unit measures 0.120-0.225 micro-Sieverts per hour. Lots of clicks from the thing aren't so scary unless they're coming from YOU, or the clicks are measured AT you from somewhere else. Or worst, the thing doing the clicking is piles of dust blowing around. Only gammas and maybe neutrons go very far through the air. Neutrons aren't as easy to measure with these tools.

David Ashton
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re: Is that a Geiger counter in your pocket (or are you just happy to see me)?
David Ashton   3/25/2011 10:41:25 PM
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My understanding is that geiger tubes will detect beta particles (electrons) and to a lesser extent gamma rays (super high frequency Electro magnetic radiation) but not alpha particles (helium nuclei) as they will not get through the glass of the tube. I think one click equals one particle of a certain energy. Or one pulse of current that produces the click, the more sophisticated (and pricey) ones just have more and more sophisticated ways of counting the clicks. I guess you could take your counter along to a university lab somewhere and calibrate it. And a man of your calibre could easily get an output and feed it to whatever you want to count the pulses later if you get that into it... Just been reading up a bit on this on Wikipedia and others, it's a huge and confusing subject. The article on Sieverts (which is what your chart has Max) says that Alpha particles have a much higher weighting than other radiation as regards damage to human tissue (which is what Sieverts are intended to measure) but they don't go very far. Apparently you should get a background count of a few pulses per minute, caused by cosmic rays and residual radiation in just about everything. I think when you get up to a few clicks per second you need to start worrying.

Max The Magnificent
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re: Is that a Geiger counter in your pocket (or are you just happy to see me)?
Max The Magnificent   3/25/2011 9:01:03 PM
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The only downside is not knowing how many clicks equate to something serious -- but still and all, it might just be handy to have one of these lying around (I bet I'd be the only guy on my street with one :-) But I think you're right -- I'll order one and build it and report back in a future blog.

David Ashton
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re: Is that a Geiger counter in your pocket (or are you just happy to see me)?
David Ashton   3/25/2011 8:38:41 PM
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There are some good kits there...at those prices, why reinvent the wheel? I'd probably go for the $79.95 one unless I was doing some serious stuff. I see a replacement tube costs the same as the whole kit...such is life these days....

Max The Magnificent
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re: Is that a Geiger counter in your pocket (or are you just happy to see me)?
Max The Magnificent   3/25/2011 8:06:21 PM
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My chum Brian just pointed me at some relatively inexpensive Geiger Counter kits (http://bit.ly/dSuRpM). Now I have to decide which one...

David Ashton
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re: Is that a Geiger counter in your pocket (or are you just happy to see me)?
David Ashton   3/25/2011 11:26:21 AM
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Well if I wanted one I'd build it myself! You can pick up geiger tubes for around $ 20. Then you need a power supply giving anywhere from 500V up to 1000V+. Small inverter running off a battery. Then you need anything from an amplifier and a speaker upwards - I'd probably put a monostable and a meter or maybe a counter circuit. (You could find a way to put an FPGA in this bit, Max...) If you're like me, you'd have most of the bits lying around except the tube, so it wouldn't cost a bomb (atomic or otherwise...) Testing it is a problem - you can buy a bit of Cesium (I'm sure us of British descent call it Caesium?) which has a 30 year half life for around a hundred bucks apparently. Though I'm sure you could find a friendly lab somewhere which would let you test it. However Australia (although they make a mint selling uranium to the nuclear powers) don't have nuclear facilities themselves (we use dirty old coal for power...) so unless the Japanese fallout works its way down here a la "On The Beach" I probably wouldn't need one....

Max The Magnificent
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re: Is that a Geiger counter in your pocket (or are you just happy to see me)?
Max The Magnificent   3/24/2011 11:43:52 PM
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I still think that the way things are going these days it might be useful to have a Geiger counter in the house. So do you know of small, good, affordable unit?

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