[ RadSafe ] GM saturation leading to failure

[Walt Cofer]

I researched this issue a few years back when evaluating the practice of some industrial radiographers to leave an extra GM meter by the radiography camera during exposures.   I spoke to Kevin Smith of NDS Products, who said that tube saturation is no longer an issue with modern tubes; they are unlikely to fail.

However, he added that routine use of a GM meter in a very high gamma/X-ray radiation field can dramatically shorten the life of the GM tube; tubes have a typical life span of ~10E12 counts, so leaving a GM meter in a high gamma/X-ray radiation field will unnecessarily increase the no. of counts the tube measures, thereby shortening its lifespan; the neon-halogen quench gas is “killed” – it loses its ability to get excited by ions (~35 counts at 1 mR/hr).

For your purposes, I believe that a GM meter will hold up fine, though if one is available, I'd recommend going with a high-range ion chamber.

Walt Cofer
Radiation Control, Inc.
Tallahassee, FL
Tel:    (850) 668-8559
Cell:   (850) 519-5351
Fax:   (850) 893-2566
Email: radcontrol at embarqmail.com
Web:  www.rad-control.net


----- Original Message -----
From: Ross Beveridge <rgb at rrbev.co.uk>
To: Radsafe <radsafe at radlab.nl>
Sent: Wed, 4 Jun 2008 06:52:07 -0400 (EDT)
Subject: [ RadSafe ] GM saturation leading to failure

Radsafers
 
I've encountered some training material that discourages/prohibits the use
of a GM contam instrument for radiation field detection.  The reason cited
for this is GM tube failure.  Having used this method in the field (in some
significant radiation fields) I'm not convinced this is a significant
problem, when used in an operational monitoring context.
 
Any further information/actual experience would be great.
 
Thanks in advance
 
Ross
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