Re[2]: Radiation Detector Calibrations

["Eric L. Darois" <daroiel@naesco.com>]

     NCRP 112 contains some good guidance on this topic.  Here is my 
     opinion.
     
     If one uses the instrument for measuring exposure rate, calibrate for 
     exposure rate to a similar (or approximately similar) energy source.  
     This should negate having to ensure that a compensated GM tube is 
     used.  If you have a wide variety of energies, compensation becomes 
     very important.  For ranges not able to be calibrated due to source 
     restrictions, use the pulser but make sure you include a "crossover 
     point(s).
     
     If the instrument is used for contamination surveys only, pulsing is 
     practical.  However, be you should verify the tube operates at high 
     rates with actual radiation.  For halogen quenched GM tubes the gas 
     can "leak-out" thereby resulting in double pulsing of an extreme 
     over-response. The pulsing process is very good for linearity checks 
     of the electronics.  In any case, for contamination monitoring, an 
     appropriate efficiency is quite important (both energy and geometry).
     
     Just a caution, the ludlum models 2 & 3 can be ordered with a wide 
     variety of meter-faces.  Some have cpm only, some have mR/hr and cpm, 
     some have mR/hr only.  The faces are designed to operate with specific 
     probes.  Almost any GM detector can be adapted to be supported by 
     these instruments.  If this is done, user beware !!!  The only scale 
     that has any meaning may be cpm, not informative for worker 
     protection...  
     
     
     Eric Darois, CHP


______________________________ Reply Separator _________________________________
Subject: Re: Radiation Detector Calibrations
Author:  radsafe@romulus.ehs.uiuc.edu at Internet
Date:    6/26/96 12:55 PM


I would be interested in any responses you get on this subject.  We have always 
calibrated our instruments in mR/hr with a Cs-137 source.  But no one here uses 
Cs-137 and most of our usage is P-32, S-35, P-33 or I-125.  For this reason, 
we are considering calibration of the instrument's CPM scale using a pulser 
and then determining the detection efficiency of the individual probes for 
the particular isotopes in use.  Does anyone out there have references 
(regulatory or otherwise) that would favor one method over the other?
     
Chris Hogan
Health Physics Technologist
University of Arkansas for Medical Sciences 
Occupational Health and Safety
cchogan@life.uams.edu 
or 
chogan@colan.uams.edu
     
All opinions are my own...
This has not been read or approved by my employer... 
This has not been read or approved by my employer..
     
From: Eric A. Goldman
     
I am trying to determine the "best" way to calibrate a survey instrument...