Re: GM Response (formerly Respect)

[Joel Baumbaugh <baumbaug@nosc.mil>]

	RADSAFERS

	I just checked my Ludlum-3 with a Pancake

	I get a "smidgen" (a scientific term if I ever hear one) under 6% efficiency with a C-14 check source and I get about 8% with S-35.

	As a caveat - One can get surprisingly good efficiency (close to 50%) with high energy betas (e.g. P-32 and/or Sr-90) if you are on a hard flat surface because the betas actually bounce back from the surface into the detector (enhancing the response).  This would not be the case with a check source which would contain the P-32 (you only get about 35% eff.) but with a contaminated surface like a lab-bench top which could/would/will interact with the surface you get more "bang for your buck"...

	I did detect bremstrahlung from a new tritium sign containing 25 Curies of tritium once.  I was impressed!	

	Joel Baumbaugh (baumbaug@nosc.mil
	SSC-SD


At 08:56 AM 9/4/98 -0500, you wrote:
>My sources indicate that C-14 has an Emax of 0.156 MeV and 
>Eavg of 0.049 MeV  compared to S-35 with an Emax of 0.167 MeV 
>and Eavg of 0.048 MeV.  So, can anyone answer why a Ludlum 
>Model 3 with a pancake probe (or any other ratemeter with a 
>pancake probe) would be "good" for C-14 but not S-35?  I would 
>think that an instrument that measures C-14 at 5 - 12% efficiency 
>would measure S-35 as similar efficiency.
>
>BTW, a year or so ago, Wes Dunn posted a table of typical 
>efficiencies of GM detectors for various isotopes.  It might be worth 
>checking the RADSAFE Archives for this info.
>
>
>Kent Lambert
>lambert@auhs.edu
>
>Peter Skeels wrote:
>
>A Ludlum Model 3 with a pancake probe is a decent instrument for 
>medium to high energy betas.  It has an average efficiency of 5% 
>for C-14 and 15 to 20% for P-32 and Si-32.  S-35 is only detectable 
>in large   quantities, so I wouldn't use it for self surveys after jobs.  
>
>
>lambert@auhs.edu
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>

Joel T. Baumbaugh, MPH, MHP
baumbaug@nosc.mil
Radiation Safety Officer
SSC San Diego, CA


	NOTE:	The contents of this message have not been reviewed, nor approved by the Federal Government, the U.S. Navy, my bosses or my wife... 


	Thought of the day...

	On the other hand, you have different fingers.
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