Re: GM Calibration Question

[Jim Vandergrift <jfvande@yahoo.com>]

The standard rules I have always used are:
(1) the orientation of the probe to the calibration
beam (field) is the same as the orientation normally
used in actual surveying regardless of the detector
type, and
(2) GM detectors are very energy dependent, when
attempting to use them for exposure measurements
(mR/hr) and must be calibrated with a radiation
source, as near as possible, to the radiation you
expect to use the detector with. 



--- Malek Chatila <mc02@aub.edu.lb> wrote:
> 
> Dear All,
> 
> I have few related questions concerning the
> calibration of GM probes that I
> hope you might clarify for me.
> 
> 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? 
> 2. When calibrating a pancake GM probe, the pancake
> window is placed
> directly facing the beam, is this correct?
> 
> 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. 
> 
> 
> Thank you in advance for your assistance.
> 
> Sincerely,
> 
> Malek Chatila
> American University of Beirut
> Email: mc02@aub.edu.lb
> 
> 
> 
> 
>
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