RE: GM counter and Two-Way Radios

[Wes Van Pelt <vanpelt@ios.com>]

Hi Radsafers,

You mentioned negative readings on a Victoreen pressurized ion chamber ratemeter.  I have a Victoreen 450 and a 450P.  Both have digital meters and do NOT have a plus/minus sign to indicate negative readings.  That is, if the device drifts negative, the numbers on the meter just get higher.  The only way I know of to test this is to bring a small radiation source close to the chamber and watch the readings go down, thru zero, and up again.  I have mentioned this to Victoreen many times, but they apparently have not corrected this design flaw.

Wes Van Pelt, CHP
vanpelt@ios.com

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From: 	Alex Zapantis[SMTP:a.zapantis@qut.edu.au]
Sent: 	Monday, October 23, 1995 6:28 PM
To: 	Multiple recipients of list
Subject: 	Re: GM counter and Two-Way Radios


>>We did the same thing using a Victoreen 450P (pressurized ionization 
>>chamber), whilst making measurements of radiation from a linear 
>>accelerator.  The meter actually registered way down (negative, with 
>>readings in milliR, as it is a LCD equipped meter). 

Is it possible that your ionisation chamber has become "wet" somehow? That
might explain negative readings. Victoreen makes an RF shielded ionisation
chamber detector. Is the 450P that one? I can't remember.




                        Alex Zapantis
                        Radiation Safety Officer                               
                        Queensland University of Technology          
                        Health & Safety Section                             
                        Locked Bag No.2
                        Red Hill Qld 4059
                        AUSTRALIA

                        Ph     : 61 7 864 3566
                        fax     : 61 7 864 3993
                        email  : a.zapantis@qut.edu.au