Russell,

You also need to take into account the relative percentages of each radiati=
on type and energy.  Betas from Am241 are negligible.

On Sep 16, 2010, at 10:29 AM, RussellMc wrote:

>> Thanks for the replies - I think I figured it out. When I put the
>> probe about 2 cm away, I get about 2000 CPM. At this distance,
>> inserting paper makes no difference and inserting copper sheet makes a
>> small difference. However, if I put the probe about 8mm away, I get
>> more than 30000 CPM and at this distance, inserting a single sheet of
>> paper cuts the count way down. I think I was seeing gamma at 2 cm away
>> and at <1cm, I am seeing the alpha as well.
>=20
> You don't think that the Beta will also feature ?
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> Beta 0.052 MeV  ... able to penetrate through several feet of air, or
> several millimeters of plastic
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> Gamma 0.033 MeV  ...  Depending on their energy, they can be stopped by a=
 thin
> piece of aluminum foil or ... penetrate inches of lead.(not in your case =
:-) ).
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>=20
> Your description of what you observe doesn't seem to exclude Beta
> playing a part.
> Adding an electric field would help to test this. Just maybe you could
> modulate the field and look for corresponding GM output modulation for
> Beta but not Gamma.
>=20
>=20
>            Russell
> --=20
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>=20

Chris Smolinski
Black Cat Systems
http://www.blackcatsystems.com




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