Re: H-3 - another theory

[Bruce Busby <bbusby@umich.edu>]

Very good point. Reality has its surprizes, and as anyone in the field 
can tell you, calculations tend to work out on paper better than on a 
meter. 

-Bruce Busby           

On Tue, 2 May 1995 ELMCGUIRE@life.uams.edu wrote:

> Let me throw another possibility out:
> 
> Electrons, contrary to what is commonly believed, or at least what is
> convenient to assume, DO NOT have a finite range.  Other processes other than
> the CSDA range are involved - straggling, etc. See Turner or any of Berger's
> work. The upshot is that you can have some penetration of electrons at depths
> >> CSDA range. Think of it like a tunnelling effect. For example, see Table 9 
> of MIRD 5; the x90 for a 20 kev 
> electron is 6E-4 cm in water. Now, a 1 mg/cm^2 wall is about 10E-4 cm, assuming
> unit density.  So, if you have a large enough activity source, even with few
> particles at or near Emax, and a container and detector with walls > range,  
> I'll bet you're detecting some H-3 beta particles.  
> 
> I've seen this phenomena with P-32; don't try shielding 100 mCi with 1 cm
> lucite - you'll need more.
>    
> 
> Lynn McGuire
> Univ. of Ark. Med. Sciences
>   
>