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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
information can be accessed at http://www.ehs.uiuc.edu/~rad/radsafe.html