[ RadSafe ] beta-gamma coincidence

Dixon, John E. (CDC/ONDIEH/NCEH) gyf7 at cdc.gov
Tue Aug 9 14:48:14 CDT 2011

Have you checked your operating voltages? Does your unit use some kind of coincidence detection? You might have a light leak or the detector window may be contaminated. Running a voltage plateau might be a good idea. At the lower voltage setting, there should be no beta counts. Gamma counts should also not be a problem until the detector is at the correct beta voltage and you have a significant gamma background problem. I have witnessed alpha to beta cross-talk when using a phoswich detector, not a gas proportional detector that is properly set up.

John Dixon

-----Original Message-----
From: radsafe-bounces at health.phys.iit.edu [mailto:radsafe-bounces at health.phys.iit.edu] On Behalf Of Michael E. Kitto
Sent: Tuesday, August 02, 2011 8:07 AM
To: radsafe at health.phys.iit.edu
Subject: [ RadSafe ] beta-gamma coincidence

Does anyone have experience or knowledge regarding the possibility (and
magnitude) of K-40 (beta and gamma emitter) producing counts in the alpha
region-of-interest (ROI) on a gas proportional detector?   I have observed
very small (0.15%) "cross-talk" from the beta ROI to the alpha ROI, but as
many of you know, even a small alpha count rate produces a noticeable
activity due to the low efficiency of GP detectors for alpha detection.

 Michael Kitto
 Nuclear Chemistry Laboratory
 Wadsworth Center, NYS DOH
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