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

[ludwik kowalski <kowalskil@mail.montclair.edu>]

On Sep 21, 2009, at 10:04 AM, Edmiston, Mike wrote:

> I was not available over the weekend when much of this discussion  
> took place.  I actually do this experiment in a home-made vacuum  
> chamber and using an alpha source from a smoke detector.  It works  
> extremely well and points out several interesting facts about  
> detection of radiation with Geiger-Mueller tubes.
>
> A photograph of the home-made apparatus, and a fairly detailed  
> explanation, and some actual data and graphs are available on my web  
> space.  If you are at all interested in this topic, I recommend that  
> you take a look at this document.  It is two pages of text plus two  
> graphs, and is in PDF format.
>
> Here is the link...
>
> www.bluffton.edu/~edmistonm/AlphaISL.pdf

Dear Mike,
1) Thanks for sharing a useful document. Referring to high counting  
rate, you wrote: "The dead time is so high for the 1-cm separation  
that this data point is not reliable and cannot be used." I suspect  
that even if a much faster counter were used (much smaller dead time  
correction), the data point for r=1 cm would still not fit the 1/r^2  
line as accurately as your other data points. The diameter of your  
Am-241 is probably close to 0.5 cm. A point-like approximation for the  
N(d) is not good at r=1 cm. A realistic N(d) relation, for a source  
that is not point-like, can be obtained via Monte Carlo simulation;  
some students might be able to do this.  I am only guessing what the  
result would be.

2) I would like to see the energy spectrum of alpha particles from a  
smoke detector source. Such sources are probably coated with thick  
layers of something (to prevent contamination and to maximize the  
ionization density). My guess is that the initial energy of 5.5 MeV is  
reduced to something like 4 or 3 MeV. Unfortunately, I do not have an  
energy calibration system.  What do you know about the energy spectrum  
of alphas from a smoke detector?

- - - - - - - - - - - - - -
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