RE: Peak shift in NaI spectrum of an Oxford Instrument MCA

["Frame, Paul" <FrameP@orau.gov>]

I tend to agree with Tom that an unstable power supply is the likely cause
of the gain shift.

Still, I wouldn't rule out the possibility that a couple of things are at
work. Something that hasn't been mentioned is that the gain of a NaI
detector system is reduced at high count rates.  If the original energy
calibration was performed at low count rates using low activity sources and
the cesium source you refer to is hot, say a few mikes, the peak might well
end up around 620 keV. Moving the Cs source further away from the detector
might solve the "problem"

Paul Frame
Professional Training Programs
ORAU
framep@orau.gov
http://www.orau.gov/ptp/ptp.htm
 
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