Re: shielding for 86-Rb

[paquette@shaman.nexagen.com (Tom Paquette)]

Our experiments shielding 32-P (1.7 Mev beta) indicate that a sufficient
thickness of lead (0.062" or greater) is more effective at eliminating
32-P betas and whatever bremstrahlung are produced by it than by using
a layer of Plexiglass in an effort to convert the betas to bremstrahl-
ung. I am not sure why this is true and the "data" is all empirical
having been obtained with Ludlum pancake GM 44-9's and low-energy gamma
PMT 44-3's.  It would be nice to redo the experiments with a high-energy
gamma probe such as a Ludlum 44-2 but the poor high energy efficiency
of the 44-3 would seem to be a neutral factor in comparing lead in
comparing lead vs. Plexiglass bremstrahlung.  I wonder if the "lead
makes bremstrahlung" statement is not more the reflection of the
behavior of thin films than thick.  Then of course there's the matter
that the bremstrahlung from Plexiglass is by my estimates somewhat
less hazardous than the betas from 32-P, but that is a separate topic.
Most folks here lead line their plastic coffins for 32-P.
   By the way, in the same set of experiments we found that aluminum
hot-blocks were fairly efficient bremstrahlung generators, I assume
because they are poor at stopping the X-rays but also perhaps efficient
at generating them.  I have not resolved which it is.  Especially, it
is important not to put one's face over the top of a hot block with
32-P in it.

-- 
Tom Paquette, PhD
Senior Scientist, RSO
NeXstar Pharmaceuticals
2860 Wilderness Place
Boulder, C0 80301
paquette@shaman.neXstar.com
biinsite@ix.netcom.com
303-546-7626
Fax 303-444-0672