Re: shielding for 86-Rb

[Michael Kay <mikekay@teleport.com>]

Rhonda O'Keefe wrote:
> 
>     I am not a health physicist, and so am seeking the help of those on this
> list who may have experience working with isotopes that are both beta and gamma
> emitters.  I would like to know what sort of shielding is appropriate for
> someone working with around 1mCi of 86-Rb in a research lab situation.
>     The advice I have been giving is to treat it like a pure beta emitter and
> use plexiglass for primary shielding, since most of the emissions are betas.
> However, the user plans to treat it like a gamma emitter and use lead (i.e. lead
> shielding around the source, wearing a lead apron).  Is the best solution to use
> plexiglass as a primary shield with lead as a secondary shield?  Any help will
> be appreciated!
> 
> Rhonda O'Keefe
> rhonda_okeefe@cambneuro.com
There is a very real possibility of an extremity overexposure the way
your experimenter wants to shield this nuclide. The high energy betas
emitted will cause bremmstrahlung and X-rays from the lead close to the
source. I once made that mistake years ago, and ended up with no
measurable dose to the 3 body badges I was wearing, but over 25 Rem to
the hands from the lead X-rays and bresstrahlung (the photons produced
by the betas slowing down in matter, the higher the Z of the matter, the
higher energy the bremsstrahlung photon energy). I would put at least
2.5 cm of plexiglass or lucite, or polycarbonate around the source,
including underneath - 5 or 6 sides. Then lead shielding for the gamma
rays will provide the necessary protection for the workers, and other
offices if needed.  Be sure that you know what is on the other side of
the wall at the back of the work area. It also would not be a good idea
to have the counting room on the other side of this work area. 

This is one time when it is necessary to use the physics of interaction
of radiation with matter to determine the proper shielding. More lead is
not the answer, a properly designed shield is the answer.

Michael Kay, ScD, CHMM
mikekay@teleport.com