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4 Posts

Posted - 07/27/2020 :  18:06:21  Show Profile  Reply with Quote
Hi all. Couldn't find an easy answer. Hopefully you can helpe out.

I just got a 600+. Are there any easy ways to filter alpha, or beta, or gamma, or x-ray?

Just trying to identify what kind of signal is hitting the tube. I know I can use paper to block alpha sources, but it there an easy way to block x-ray and allow alpha?

That's the kind of stuff I'm looking for

Thanks for any help.
Reply #1


241 Posts

Posted - 07/27/2020 :  22:48:42  Show Profile  Reply with Quote
I don't think, so, there is always a solution to take two measurements ('alpha + gamma', and 'gamma alone') and do a substraction.

Mastery is acquired by studying, with it everything becomes simple

Edited by - Damien68 on 07/28/2020 23:37:37
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Reply #2


19 Posts

Posted - 07/28/2020 :  17:12:38  Show Profile  Reply with Quote
Unfortunately a material that allows alpha but not other types of radiation through it is pretty much a physical impossibility as far as I know. Alpha particles are much heavier and slower than beta particles and especially gamma and x rays, so the only way you can measure just alpha radiation is to use a dedicated (and very expensive) alpha scintillator.

That said, the subtraction method is a decent enough "workaround"... At least for low level sources, maybe. At the very least, you can use this method on readings from an alpha sensitive model (such as the 600+) to determine the primary type of radiation (alpha or beta/gamma*) emitted by any given source.
* - gamma and x rays are both just high energy photons, gamma being the most energetic and most penetrating radiation

Of course, there are really only two primarily alpha emitting sources that you're likely to come across even if you're looking for them: smoke detector americium 241 "beads", and StaticMaster brushes (and refills), which use polonium 210. IMHO the latter are not worth buying: refills are as much as 50 bucks a pop and with a half life of only 138 days they're useless in a year or two.

On the other hand, a smoke detector is like 5 bucks - just be sure it has the radiation warning and symbol somewhere on the box. ;) The half life of Am-241 is also an amazing 440 YEARS, so they are really good value for money to make this detector go crazy. A single source has the potential to crash it if you don't turn dead time off!

Other than that, anything with uranium, thorium, or radium in it is also going to contain "daughter isotopes" which over time become the main source of radiation. Here is an article on thorium:
The other elements behave similarly, though I'm not sure of exact time frames.

I also have a TG-48 spark gap tube with "<5 microCuries Cs-137" which is about as good a gamma source as you can get, and two Sr-90 check sources from DP-63-A portable Russian Geiger counters for pure beta. Scary, btw, if you don't know what you're dealing with...

Have fun but stay safe!
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Reply #3


491 Posts

Posted - 07/30/2020 :  01:55:24  Show Profile  Reply with Quote
Unfortunately, there is no way to block x-ray ( = gamma) and to allow alpha or beta. Going for blocking alpha with a sheet of paper, then also blocking beta with a few mm of aluminum, or a few mm of copper, or a stack of paper sheets, and measuring the remaining count rates, and doing the subtraction, is the only option.

But this may bring errors of its own, and under certain conditions seemingly blocking some radiation may result in HIGHER counts rather than lower! The key word here is Bremsstrahlung. The effect depends much on your radioactive sample(s) and your experimental setup(s).

Find some intro in chapter "Appendix Range of Electrons in Matter and some History" of my Potty Training article
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Reply #4


4 Posts

Posted - 08/04/2020 :  17:43:15  Show Profile  Reply with Quote
Thanks all! That's enough for me to work with!
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