Re: GM calibration question

[Steve Frantz <sfrantz@aone.com>]

Les Slayback has made an important point about using GM tubes to measure dose rate (or
exposure, or dose equivalent). To measure any of these parameters you need the correct
instrument: ion chamber, energy-compensated GM, etc. In my opinion you should not try to
use a regular GM tube to measure dose. A lot of the discussion on the list has been on
techniques to make a GM detector indicate dose. The trouble is, it never _really_ works in
the field.

At our facility, the GM tubes are all calibrated for cpm and an efficiency is determined
so the operator can determine dpm (or Bq). GM detectors are only used for contamination
surveys. We ignore the mR/hr scale on GM instruments. We gave away the GM's that only had
a mR/hr scale.

To determine dose we use ion chambers, NaI detectors, energy-compensated GMs, etc.

This requires having two types of detectors, but if you're measuring two different
parameters (dose and contamination), that's what you have to do.

Stephen Frantz
Reed College Reactor
3203 SE Woodstock Blvd.
Portland, Oregon 97202
503 777-7222
fax: 503 777-7274
mailto: sfrantz@reed.edu


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