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Re: [Phys-l] Alpha decay intensity against distance




On Sep 19, 2009, at 4:15 PM, John Denker wrote:

On 09/19/09 06:22, Savinainen Antti wrote:

BTW, what radioactive source could be used for this experiment as
there usually are daughter nuclei present emitting gamma and/or
beta radiation?


Off the cuff, my first idea would be to use Americium 241.
There's a reason they use it in smoke detectors.
It has a half-life of 432 years,
http://atom.kaeri.re.kr/ton/
so unless it has been sitting around for a rather long
time, you don't need to worry too much about daughters.
Also the daughter has a half-life of a couple million
years, so it wouldn't contribute much to the rate even
if some of it were present.

1) Alpha particles at 0.5 meters away from the source (in normal air) were mentioned in the original message. Was it a typo? If not then pulses were perhaps due to alpha particle from radon (in air) or to something related to cosmic rays.

2) Am-241 also emits 59 keV X-rays.

3) The dependence of counting rate on distance in air, N(d), would be 1/r^2 (from a point source in good vacuum) and alphas would be detectable at 0.5 m.

4) Suppose a beam of parallel alpha particles enters into air. In this case the N(d) (d=distance traveled in air) would be flat till the average energy becomes about 2 MeV. After that the counting rate starts going down. But the curve is not exponential. Some particles travel longer distances in air than others.

P.S.

New unit has been posted at my CF website:

http://csam.montclair.edu/~kowalski/cf/376kitamura.html

Comments, as always, will be appreciated.

- - - - - - - - - - - - - -
Ludwik Kowalski, a retired physics teacher and an amateur journalist. Updated links to selected publications and reviews are at:

http://csam.montclair.edu/~kowalski/cf/ http://csam.montclair.edu/~kowalski/my_opeds.html http://csam.montclair.edu/~kowalski/revcom.html

Also an ESSAY ON ECONOMICS at: http://csam.montclair.edu/~kowalski/economy/essay9.html