RE: GM probe efficiencies

["Jim F. Herrold" <Herrold@UWYO.EDU>]

Bob Milwicz asked:


> If the commonly used isotopes are:
> 
> C-14, S-35, P-32, P33 and Ca-45 which are all beta emitters and if a
> survey meter like the Ludlum Model 3 with a Model 44-9 pancake probe
> are being used for surveys, what are the counting efficiencies that
> you use to determine the activity present and at what distance from
> the source are you determining your efficiency? 
> 
As a follow-up to my last post... This is a good point, which I failed to
mention. We don't want our people to drag their detectors through the
contamination, so our Radiation Safety Manual suggests a survey distance
within one inch. Therefore, when we calibrate the instruments, we give the
beta efficiencies on contact and at one inch. It makes quite a difference.
As an example, one detector had a 8.9% efficiency for C-14 on the surface,
but 0.7% at one inch.

Jim Herrold, Radiation Safety Officer
herrold@uwyo.edu

University of Wyoming
Environmental Health & Safety
303 Merica Hall
Laramie, WY 82071-3413

(307) 766-3277
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