Re: shielding contaminants

[jgbarnes@ix.netcom.com (JAMES BARNES)]

Dear Dr. Low,

I was always told to use pre-WWII battleship armor plate for low-level shielding 
(there was no Cs-137 fallout contamination).  That was tens of years ago, so I 
don't know if it is still available (It was sometimes hoarded by the more 
"nuclear aware" scrap dealers, so you might still be able to find some).

You might want to take a look at using electronic methods to reduce your 
background rates, however.  After a certain level of shielding, the use of an 
anti-coincident detection circuit may serve you better (and be more cost 
effective) than another inch or two of lead.  (See Knoll, "Radiation Detection 
and Measurement; Second Edition", p. 643 and p. 730 for a discussion of the 
principal).


Jim Barnes, CHP
RSO
Rockwell Aerospace; Rocketdyne Division
------------------------------------

You wrote: 
>
>I have a rather unusual shielding problem to solve.  I have to shield some 
>scintillation detectors from ambient background radiation, and want to do it in 
>the most cost effective manner.  The radiation level has to be reduced by a 
>factor of 1000.  I have determined the thickness required of lead, steel, and 
>concrete (in order of decreasing cost) to provide this level of shielding for a 
>1 MeV photon (the average background gamma energy I used for the shielding 
>calculations).  However, I am concerned that I will be adding as many background 

>gammas from the shielding material that I am removing if the shielding material 
>has low-level radiation in it.  Does anyone know which of the three alternatives 

>will provide the least background?  What are the level of contaminants in the 
>proposed shielding materials relative to "normal" soil?
>
>Thank you in advance,
>
>Daniel Low, Ph.D.
>
>
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