GM probe efficiencies

["Robert R. Milwicz" <milwicz@arundel.Princeton.EDU>]

GM probe efficiencies

Kent Lambert beat me when he posted the question about why a GM
could be used for C-14 and not S-35! I was going to ask that question
myself and this additional question.

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? I raise this question
because I hear different efficiencies when I ask other people this
question.

One reason could be the type of screen covering the window face. I
understand that Ludlum might have used 4 different screens over the
years. Of course, there are other reasons like the calibration source
used, its geometry, and its distance from the meter.

Any way, if you feel this comparison between meter users is worth
while, respond to me, I will summarize the data and post it.  What
prompted me to ask is the comment about the S-35 in the post Lambert 
responded to and also the post that just arrived in which Joel  
stated what he found as the efficiency for C-14.

 I hope to hear from you. Any I will post the summary. 

Thanks for your responses ahead of time, 

BOB Milwicz
Milwicz@princeton.edu 
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