Fluke Biomedical 943-35 - Manual (Page 18)

Victoreen 942-35,943-36,943-36H, 943-37,943-237A
Operators Manual
4-4
943-35, 943-36, 943-36H 200 CPM
943-37 400 CPM
943-237A 3000 CPM
3. Place a 133 Ba button source (P/N 844-36-15), blank side up in the slide drawer of the standard
geometry, and insert drawer into geometry.
4. The expected count rate for the button source should be determined. It is recorded on the factory
calibration data sheet. Correction must be made for decay. (The half-life of the source is 10.74
years).
5. Run a 2-minute count (10,000 CPM minimum), using the 133 Ba source.
6. Adjust the high voltage power supply to the detector so that the net count rate corresponds to the
expected count rate calculated in step 4. (Net count rate is indicated count rate minus background
count rate). A ± 2% tolerance is acceptable.
7. The count rate will increase and decrease in conjunction with the high voltage setting. If the high
voltage reaches the maximum allowable setting without achieving the necessary count rate,
suspect a defect in the detector, wiring or readout device.
8. If additional button sources were provided, repeat step 5 for each source. A 6% tolerance is
acceptable.
9. If the above sources are not within ± 6%, the gain may be incorrectly set on the 356 keV 133 Ba
photopeak and not on the 80 keV 133 Ba photopeak. Using a 137 Cs source and an oscilloscope, verify
and adjust the high voltage so that the 137 Cs photopeak is at approximately 2.3 Volt average (1.65
Volts for Americium regulated detectors). Step 6 should then be repeated being sure to adjust the
high voltage in the negative direction only.
Calibration Without Transfer Button Sources
In the event secondary transfer sources are not available, the detector high voltage may be set to the
value stated on the calibration data sheet by using a
137 Cs source and an oscilloscope. The average
height of the 137 Cs photopeak is approximately 2.3 Volts, at the high voltage stated on the calibration data
sheet, and may be checked to determine proper detector alignment. Without a set of secondary sources,
however, the overall detector response in terms of counts per minute, μCi per cm
3 must be determined by
the user's primary calibration.
4.3 Troubleshooting
Extreme care must be used when troubleshooting a
system that has power applied. All standard
troubleshooting precautions apply.
Extreme care must be used when troubleshooting
in close proximity to the high voltage output.
Once a problem has been located, remove all
power before continuing with the repair.
WARNING
WARNING
WARNING