RE: GM Calibration Question

["Joey Michael" <jmichael@blue.weeg.uiowa.edu>]

> > 1. When calibrating an open-end window GM probe, the probe is placed
> > perpendicular to the beam axis, i.e. the window is not directly 
> facing the
> > radiation beam, is this correct? 
> 
> Generally, yes although it really depends on how you plan to use 
> the instrument
> 
> > 2. When calibrating a pancake GM probe, the pancake window is placed
> > directly facing the beam, is this correct?

 Generally yes

> > The problem that I am having is the following:  when trying to 
> calibrate a
> > pancake probes that are coupled to Victoreen's THYAC IV survey 
> meters, the
> > meters constantly over read by 50 % when the pancake probe window 
> > is placed
> > facing the radiation beam while an accurate reading is obtained when the
> > pancake probe handle is placed perpendicular to the beam axis i.e. the
> > window facing down and the beam axis is horizontal.  
 
 Call Victoreen 1-800-850-4608.  A lot of victoreen instruments 
 use a correction factor depending on the meter and probe 
 combination.  I have also had experience where Victoreen said to 
 turn the pancake probe perpendicular (beam intercepting the side) 
 to the beam.

 Hope this helps
 

Joey Michael
mailto:joey-michael@uiowa.edu
University of Iowa
Health Protection Office

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