Re: GM Meter Calibrations

[avest@magnus.acs.ohio-state.edu (Albert Lee Vest)]

>All of our GM Counter calibrations are done in house using a Cs137 source. 

Sounds just like our operation.  We've got a number of NaI's and AIC's, too.

>This necessitates many hours of holding probes in the "beam" and making small
>adjustments in position to get the most optimal reading. Not only do the arms
>and shoulders get tired but with some of the instruments, particularly those
>with internal probes such as the SE International Monitor 4, it is difficult
>to get an accurate view of the meter.

On our range, we use a wheeled lab cart to support the instruments during 
calibration.  The floor is marked for distance from the "point" sources, in 
centimeters.  A ring stand with clamps is used to support portable probes, 
like GM's and thin NaI probes.  We've got a few small lead plates (4-in 
squares by about 3/8" thick) to weight the ring stand for stability.

For the internal-probe instruments, a mirror is used.  I think we just 
bought it from a hardware store; it's a hand-size mirror on the end of a 
folding handle, with a couple of swivels, so it's adjustable to rest on the 
lab cart and give you a view of the scale from a comfortable position. 

Different users' meters come due at different times, so we're always 
calibrating a few meters every week.   Write back if you want more info.
Albert Lee Vest    avest@magnus.acs.ohio-state.edu
health physicist        Office of Radiation Safety
(614)292-0122            The Ohio State University
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