RE: Gamma Level for Cs-137

[Glen.Vickers@ucm.com]

What is the source for the gamma constant?  We all know the values, but are
they calculated values or measurements?  Even if they are measured values,
the response characteristics of your instrument are not likely to be the
same.

Our irradiators are typically characterized with a transfer instrument which
is traceable to NIST, not calculated values based on the gamma constant.  If
you are primarily doing electronic dosimeters, then you should use that
specific instrument as your transfer instrument to account for all of the
little response characteristics of that instrument.  Such transfer
instruments will permit you to accurately and precisely determine the dose
rates of your calibration source.  I have found that you can actually get
better precision from certain models of electronic dosimeters than with
TLDs.  TLDs with certain filter mixes can, however; give you a feel for the
amount of scatter in your shielded irradiator.
 
In general I would not expect calculated values to match up perfectly with
measured values.  Instrument response is always some compromise of the
theoretical.

Sincerely,
Glen Vickers
glen.vickers@ucm.com

	-----Original Message-----
	From:	Mercado, Don [SMTP:don.mercado@lmco.com]
	Sent:	Wednesday, February 17, 1999 1:14 PM
	To:	Multiple recipients of list
	Subject:	Gamma Level for Cs-137



	> Greetings,
	> 
	> Do any of you have another gamma level for Cs-137 other than the
0.33 R/hr
	> at 1m/Ci as stated in the Rad Health Handbook? I'm having trouble
	> calibrating my pocket dosimeters and having them come in within
spec. We
	> use TLDs to check what exposure the dosimeters are getting, and
they agree
	> with the chamber readings. Unfortunately, they all are about 30%
below
	> what I've calculated they should be getting using the above
number.
	> 
	> Any help would be appreciated. Thank you in advance.
	>  
	> Donald P. Mercado
	> Radiation Safety Officer
	> Lockheed Martin Missiles & Space
	> O/47-20, B/101
	> 1111 Lockheed Martin Way
	> Sunnyvale, CA 94089
	> Ph. (408) 742-0759
	> Fax (408) 742-0611
	> Email: Don.mercado@lmco.com
	> 
	> 
	
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