F2 – Test Menu
Gem-5 User’s Manual 197
F1 – Rate Meter
The Rate Meter screen (Figure 90) displays gross count and count rates for all
detectors simultaneously during an adjustable time interval (Dwell Time). The count
rates for the Gamma Counter are shown.
Figure 90 The Rate Meter screen Provides Live Count Rates for All Detectors
The high voltage is set to its normal operating value for this test and thus is turned on
for this screen. Count rate data are displayed while the high voltage is ramping up
thus any problem with the high voltage system will be evident from the count rate.
Note that instead of trying to test them, detectors put in Conditional Service on the
F4 – Faults screen show the words “Conditional Service” in place of the data
normally shown. In addition, these detectors are greyed out.
Assuming there are no sources or contamination near the detectors, all detectors
should have similar count rate within the random statistical variation and differences
in efficiency of detectors. This screen is one of the fastest means for checking overall
system performance. If all count rates look similar and all detectors are actively
counting, then the system detection capability is normal.
If a detector appears more active than others of the same type, it could suggest the
presence of a nearby source, a contaminated area, a noisy amplifier, or a failing
detector. Conversely, a low count rate suggests a high voltage problem or decreased
detector sensitivity, pointing to an incipient detector failure, or an aging
photomultiplier tube (scintillation detector). This should be verified with a high
voltage check (F2 – HVPS Meter on page 200) and a calibration or alarm test of the
detector.
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