Re: shielding for 86-Rb

[Michael Kay <mikekay@teleport.com>]

Tom Paquette wrote:
> 
> 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

Tom,
What is the purpose of the shielding. If it is to protect those outside
of the work area, than thick lead is fine. However, if the purpose is to
provide shielding for the researcher's hands and extremities, like in a
glove  box or behind a body shield, then it makes a large difference.
The dose rate from X-rays and bremsstrahlung can be orders of magnitude
larger on the source side of a lead shield than on the source side of a
proper beta shield.

For greater shielding efficiency, it would be better to encase the poly
coffins in lead rather than line them with lead.

Michael Kay, ScD, CHMM
mikekay@teleport.com