Model 12-4 Technical Manual Section 6
Ludlum Measurements, Inc. Page 6-5 May 2016
Expose the detector to an 80 mrem/hr neutron field.
Confirm that the meter reads 8 mrem/hr on the ×10 scale.
If the reading is not 8 mrem/hr ±5%, make a slight adjustment to the HV
supply to yield an 8 mrem/hr meter reading.
Expose the detector to a 20 mrem/hr field and confirm a meter reading of
20 mrem/hr ± 10%.
Proceed to calibrate all scales with a meter reading of 2 and 8 mrem/hr.
Electronic Calibration
If your range is inadequate to equal all points between 2 mrem/hr and 800
mrem/hr, you may use a pulser to electronically calibrate the instrument.
Multiply the cpm/mrem/hr as determined on the plateau
check by the range selection and meter reading. (i.e. typically,
120 cpm/mrem/hr × 1000 × 8 = 960,000 cpm for 800
mrem/hr)
Set this calculated number in the pulser and calibrate the
associated scale.
Note on the calibration certificate that this range was
electronically calibrated.
Maintenance
Instrument maintenance consists of keeping the instrument clean and
periodically checking the batteries and the calibration. The Model 12-4
instrument may be cleaned with a damp cloth (using only water as the wetting
agent). Do not immerse instrument in any liquid. Observe the following
precautions when cleaning:
1. Turn the instrument OFF and remove the batteries.
2. Allow the instrument to sit for one minute before accessing
internal components.
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