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Create a home made muon or gamma ray detector?

by parazit
Tags: detector, gamma, home, muon
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parazit
#1
Aug3-09, 09:53 AM
P: 45
Hi.I wonder is it possible to create a home made muon or gamma ray detector? And if it is possible would you mind to show me some way? Thanks...
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vanesch
#2
Aug3-09, 12:23 PM
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Of course this is possible, if you are willing to invest a bit. I can think of 2 approaches: a Geiger counter, or a scintillation detector with some photomultiplier or cheaper, an avalanche photodiode. But in either case, you will run into a few hundred to maybe a few thousand bucks.
I don't know offhand any do-it-yourself schemes but I know how to make these things professionally, so I could have some idea...
Bob S
#3
Aug3-09, 04:58 PM
P: 4,663
If you use two Geiger counter tubes with an inch of lead or alumimum or copper between them, and plateau them to detect minimum ionizing particles like cosmic rays, put them in coincidence, using standard didital NAND or AND gates with a 100 microsecond overlap gate, you will find that the coincidence counting rate is a lot higher than you would calculate from random coincidence rate. If you could get two high-gain end-window photomultiplier tubes with bases, and two pieces of plastic scintillator, make them light tight with black tape, and put them face to face with the same lead or aluminum or copper between them, and set your coincidence gate width to 10 nanosec, and do the same thing.

hardhacker
#4
Aug3-09, 09:24 PM
P: 11
Create a home made muon or gamma ray detector?

I have been trying to build a low cost muon detector using Geiger Muller Tubes - http://www.hardhack.org.au/geiger_muller_detector so that others can build too.



However although the finished results look good enough, I'm not sure its conclusively detecting Mouns.



The output pulse of three (beta/gamma) Geiger Muller Tubes is shortened to a few microsecond before feed into a coincidence circuit. So that only an output is produced when two or more tubes have matching coincidence pulse within a few microseconds.

However the number of coincidence pulses is about 1 to 2 pulses a second which seems rather high compared to other examples I have read. Also although some changes occur I was expecting the rate to fall dramatically or to zero when the orientation of the tubes are changed from vertical to horizontal.

I have a feeling I'm missing something.

Regards

Robert
Bob S
#5
Aug4-09, 11:08 AM
P: 4,663
Congratulations on building a nice-looking GM tube cosmic ray counter array. The actual rate of cosmic rays is of the order of 1 count per minute per cm2 of active area, but it does depend on solid angle, so this number is only approximate. I will assume that each GM tube has a broadside active area about 10 cm2, so maybe 10 counts per minute is a good number.
On counting rate and accidental coincidences, it is important to record the singles counting rate for each of your tubes; S1, S2, and S3 counts per second.. If your coincidence gate width is τ seconds, then for example, your counter #1 is ON S1τ of the time, and you should have random councidences with tube #2 at a rate R12 = S1S2τ random coincidences per second. This random coincidence rate should be less than 1% of what you expect for the real coincidence rate, or about 0.1 counts per minute.
You should move the GM tubes away from your other instrumentation, to minimize noise pickup from transformers etc. Although your electromagnetic shielding looks good, it is not 100%. The GM tubes should also be shielded from one another. One reason is that discharges in one tube could affect another tube, but also some cosmic ray interactions in one tube could produce x-rays or gamma rays that can be detected by another. One example is Compton scattering, which produces a recoil gamma ray that could easily hit another tube. So putting a little x-ray shielding between the tubes; about an inch of aluminum, 1/2" copper, or 1/4" lead (but not iron), is a good idea. Another thing that is a lot more important for phototube scintillator systems than GM tubes is to alternate the directions the cables come out from each tube. You now have right, right, right. Using right, left, right is better.
I hope this helps.
Bob S

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hardhacker
#6
Aug4-09, 06:42 PM
P: 11
This is very helpful feedback thank you, yes indeed these are broadside GM tubes thin walled beta/gamma sensitive, I chose them for their larger surface area.

I had no idea about a GM tubes producing a recoil gamma ray. Compton scattering sounds very interesting. I will definitely try you suggestions luckily I have a length of 1/2" think copper busbar at the factory.
parazit
#7
Aug5-09, 04:34 AM
P: 45
Thank you so so much for your attention.I think i got lots of thinks to read and learn..
hardhacker
#8
Aug12-09, 08:16 PM
P: 11
I'm now looking into improving the RFI electronics between each of the detector amplifiers and the tolerances of pulse forming.

I tried adding shielding, at first with 25mm of Copper and then 6mm Lead between each GM tube and observed no difference, I also tried some other GM tubes and can't find any evidence that Compton Scattering cause two or more GM tubes held close to each other to cross-talk.

After doing some hunting the only reference I can find in relation to shielding and GM arrays is here http://teachers.web.cern.ch/teachers...s/cascades.htm any other advice very welcome.


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