Re: Radiation Detector Calibrations

[John Lobdell <lobdell@fly.HiWAAY.net>]

At 11:38 AM 6/26/96 -0500, you wrote:
>Time for a new topic.  
>
>I am trying to determine the "best" way to calibrate a survey instrument
(i.e. Ludlum 
>III.)  There have been two methods proposed: A pulse generator or a Cs-137
Calibration 
>source. Any information would be appreciated. 
>-- 
>Eric A. Goldman, B.S.,CNMT	
>Baylor University Medical Center
>Department of Medical Physics/Radiation Safety
>Dallas, Texas  75246
>(214) 820-3870
>
>"Gotta run, the cat's caught in the printer."
>
An instrument calibration obviously requires a known radiation field in
mR/hr or R/hr.

The Cs-137 source can be calibrated by using NIST traceable instruments like
an R-chamber or an ion chamber with electrometer.  Or the curie content of
the source can be known and the exposure rate calculated by using the
inverse square law and gamma constant.  (Scatter would limit the accuracy of
source calibration using the inverse square law and gamma constant).  The
Cs-137 field would be constant or nonvarying.  

A pulse generator is assumed to provide a varying or nonconstant field.
What is the energy of the photon or average photon emitted?  What is the
frequency?  How are you going to calibrate the field?  How is the instrument
going to respond to this nonconstant field?  If the instrument has an
analogue readout, how is the meter going to respond to this nonconstant
field?  There are too many unknowns with the pulse generator.

What energy photons are going to be measured with the instrument you are
going to calibrate?

I  vote for the Cs-137 field.  It is easier to calibrate and is the
"standard" method used to calibrate portable survey instruments.

John Lobdell, Ph.D., C.H.P.
lobdell@HiWAAY.net