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RE: Scintillation Spectroscopy



Another possibility is that the high voltage on the PMT is very high in
which case the tube becomes very sensitive to changes in barometric pressure
and the calibration shifts as you reported.

Of course, both temperature and pressure and other effects could be the
culprit.

Bill Kendall
kendall@nucuasa.com

-----Original Message-----
From: Tom Gwise [mailto:gwise@SLAC.Stanford.EDU]
Sent: Thursday, March 25, 1999 10:16 AM
To: Multiple recipients of list
Subject: Re: Question


I believe the problem you describe is caused by temperature changes over
the count time. I use a system almost identical to yours and I have had the
same problem. Try to stabilize the temperature of the electronics. I would
be interested in knowing how you resolve your problem. Please contact me at
the address below if you would like to discuss my experiences with this
system.

Tom

>Dear Colleagues!
>Could somebody make clear for me the following question?
>I am Dr.Yuriy B. Nabyvanets from National Yang Ming University, Taipei,
>Taiwan. I investigate the contents of radionuclides (Cs-137 and gamma
>emitting radionuclides from Th-232 series) in soil. I use the EG&G ORTEC
>Nomad Plus Portable Spectroscopy System, HPGe Coaxial Detector System
>(GEM Series) and Gamma Vision Software for gamma spectrum analysis.
>About two months I had not any problems with my device and it worked
>perfectly. But approximately 2 weeks ago I got some problems. As the
>contents of radionuclides in soil samples rather low, I need 8 hours to
>measure each sample.  And here approximately in 5 hours of measurements
>I have become to notice that the spectrum of samples begins to change.
>It means, that near to, for example, peak of K-40 (from the left side to
>the region of low energies) occurs the second and third peaks. That
>occurs also for peak of Cs-137 but in this case shift goes to the region
>of high energies. It seems, that during measurements  energy calibration
>varies. I check energy calibration every day and really peak of Cs-137
>>from standard source changes location on a spectrum. The difference
>sometimes reaches 10 KeV.
>So, what the possible reason of this phenomenon? I hope for your help.
>Sincerely  Yuriy B. Nabyvanets
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Thomas Gwise
Operational Health Physics
Stanford Linear Accelerator Center
PO Box 4349     MS 84
Stanford, CA 94309
650-926-4172


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The RADSAFE Frequently Asked Questions list, archives and subscription
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information can be accessed at http://www.ehs.uiuc.edu/~rad/radsafe.html