RADSAFE: Re: Self-absorption correction - for GFPC

["Donivan Porterfield, LANL CST-3" <dporterfield@lanl.gov>]

Personally, I would advise against the use of "generic" self absorption
factors in your apparent application.  The self absorption factors, most 
notably for alpha, have some dependence on the energy of the alpha 
or beta emitter one is calibrating for.  Also the elemental composition
of the solids deposited can influence the self absorption factors.  
This is not to mention the proportional counter/detector itself.

I would also say that any knowledgable auditor or data user of 
your analytical process would not look generously on such a practice.
Admittedly, you could try and prove the effectiveness of using a 
generic calibration curve.  But by that time, it would have been 
easier to just do the self absorption calibration curve.

I think that this is a case in which if you need to do the analysis,
you need to do it appropriately.  If your trying to reduce the effort
required just make a curve for the 50-100 mg range you indicated.
Minimize the number of points on the curve by using more points for 
alpha than beta.

If your set on using "generic" self absorption factors check yourself
with lab control samples (LCS) with each analytical batch.  These 
would likely prove the poorness of such a generic approach and if 
properly done create a pool of data you could use for real self 
absorption factors in the long run.

>Date: Wed, 27 Nov 1996 18:05:25 -0500 (EST)
>From: Keith Welch <welch@CEBAF.GOV>
>Subject: Self-absorption correction
>
>Does anyone know of any "generic" self absorption factors that work for
>alpha/beta counting that would help get me in the ball park for a 2"
>planchet counted in a typical laboratory low bkg proportional counter.
>I know the mass of the solids deposited on the planchet - its in the 
>range of 50-100 mg. Is there a common reference that will get me close
>without having to build self absorption calibration curves?


Donivan Porterfield                     (505) 667-4710
Los Alamos National Laboratory          (505) 665-5982 fax
MS K484, CST-3 (Analytical Quality and Chemical Information Management)
Los Alamos, NM 87545                    dporterfield@lanl.gov