beta shield sources

bart janssen bjanssen at bio.tamu.edu
Fri Nov 3 11:44:14 EST 1995


In article
<Pine.A32.3.91j.951102133948.62498A-100000 at homer08.u.washington.edu>,
Mayumi Yagi <myagi at u.washington.edu> wrote:

Both plastic and lead shield produce Brehmstrallung (X-ray) radiation as
the beta particle interacts with the shielding material.  The difference is
that with lead in the primary shield the X-rays produces are characteristic
of lead and are very high energy X-rays and hence very difficult
subsequently shield against.  With plastic (or glass or water) as the
primary shield the X-rays produced are characteristic of the Carbon (or
Silicon or Oxygen) and much lower in energy and hence easier to shield.  In
practice X-ray emision from milicurie amounts of 32P shielded by perspex is
not a significant hazard and can be shielded adequetly by a thin layer of
lead or steel (eg a fridge door).

The best way to shield 32P is with a centimeter or two of perspex as the
primary shield and then a thin (1 mm) layer of lead.  However, placing the
isotope in a perspex container in the fridge is fine.  If you're working
with greater than millicurie amounts of 32P you may need to worry about
Brehmstrallung a bit more.

Final point, the radiation hazard from 32P beta particles and any
Brehmstrallung radiation from the shielding is very low.  It makes good
sense to limit the amount of radiation you are exposed to but the radiation
dose you get from the average medical X-ray dwarfs the radiation dose you
get in the lab.

The real hazard from isotope in the lab is ingesting it, then it really is
dangerous.  So just don't eat your lunch while doing a labelling reaction
:).

cheers
Bart  

> Nicholas, 
> Is it possible that you are using a lead-impregnated plexiglas shield?  
> We have a couple on hand in our lab for 125I work, as well as "normal" 
> plexiglas for 32P.  You can't use the lead ones for 32P work--they will 
> generate Brehmstrallung radiation, as you seem to be seeing.  The lead 
> ones are slightly more yellow than the non-lead guys (they look more 
> "aged", presumably due to the lead).  The regular ones damp down 32P 
> effectively (though if you're looking at high levels, not completely).
> 
> Mayumi
> 
> On 2 Nov 1995, NICHOLAS THEODORAKIS wrote:
> 

> > 
> > Well, I don't have a recommendation (many lab supply vendors sell them),
> > but I do have an observation that I hope will generate some discussion. 
> > We have some plastic beta shields from Owl Scientific around the lab; 
> > when we were doing some rad. surveys with a monitor that has probes for
> > both beta- and gamma rays, we noticed that 32P kept behind the shield
> > generated a lot of bremstrallung (spelling?) gamma radiation when it hit 
> > the plastic (which did block the betas, BTW).  I almost think it would 
> > safer not to use the shield.  Has anybody else noticed this with their 
> > beta-shields?  Any comments?
> > 
> > Nick



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