Homemade radiation detector problem

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hsieh
 
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Homemade radiation detector problem

Post by hsieh »

I build the "ion chamber" radiation detector described in this website http://www.techlib.com/science/ionchamber.htm

I cannot find the Darlington MPSW45A so I use BC517.

I get 15~25mV reading on my multimeter.But when I put a thorium doped welding rod in front of it,nothing happen.The reading on my multimeter dosen't change at all.I even tried to put the welding rod inside the can.

I borrowed a geiger counter and verified my welding rod contains thorium.I checked everything I could and don't find any mistake.


thanks

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zener
 
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Re: Homemade radiation detector problem

Post by zener »

The pins on the BC517 are backwards compared to MPSW45A. Do you know that? You have to connect it backwards compared to the photos. The center leg is the same.

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hsieh
 
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Re: Homemade radiation detector problem

Post by hsieh »

Zener wrote:The pins on the BC517 are backwards compared to MPSW45A. Do you know that? You have to connect it backwards compared to the photos. The center leg is the same.
I know that.I think I connect it correctly.

I also noticed that when I touch the long wire connect to transistor base ,the reading on my multimeter become the voltage of the battery.
Is this means my circuit is working properly?

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neutron spin
 
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Re: Homemade radiation detector problem

Post by neutron spin »

Your DMM should have a high input impedance >10 megohms. If you are using a meter with decent specs then perhaps your build is flawed. Both transistors have fairly high HFe numbers but not sure if they will perform the same in this case. Also do not expect this type of detector or ion chamber to work as well as a regular GM tube which is designed for geiger counter use. In fact it is quite interesting that the thing even works...or does it really? :(

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zener
 
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Re: Homemade radiation detector problem

Post by zener »

They say this is a radon detector, not a geiger counter. I have no idea if this is supposed to detect Thorium.

pstemari
 
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Re: Homemade radiation detector problem

Post by pstemari »

Looks like radon does a alpha decay (5.6 MeV) into polonium and again (6.1 MeV) into lead:

http://atom.kaeri.re.kr/cgi-bin/nuclide?nuc=Rn-222
http://atom.kaeri.re.kr/cgi-bin/nuclide?nuc=Po-218

Thorium does alpha (4.1 MeV) to radium, beta (0.046 MeV) to actinium, beta (2.1 MeV) back to thorium 228, and then a series of alpha decays (5.5 MeV, 5.8 MeV, 6.4 MeV, 6.9 MeV) into lead.

Long story short, if the detector can detect one, it can detect the other, although thorium is a lot less radioactive than radon--14 billion years vs 3.8 days. Presumably you've got a bigger sample of thorium than of radon--or if not, you will shortly :D

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