A-10
back end of the instrument marks the center of the tritium chamber for alignment purposes. To ensure a uniform
gamma field, the instrument shall be at least 28 inches away from the radiation source.
Figure A-2. Calibration Setup.
a.
Record the background reading (which may be elevated since gamma compensation is disabled).
b.
Expose the Model 3100 to the desired uniform gamma field using the dimple marks on the “can” to
center the chamber. Note that the response time of the instrument is approximately one minute. If the
instrument does not read the correct value after one minute has elapsed, increase or decrease the
calibration constant for the appropriate range as needed until the correct value is reached. See Table A-
1 for recommended calibration fields. “Cal” indicates the recommended point for adjusting the
calibration constant, while “Ref” indicates where the reference reading is taken to confirm linearity.
Table A-1. Recommended Calibration Fields.
137
Cs µSv/h (mR/hr)
Tritium µCi/m
3
Equivalence
Range/Test
600 (56.4)
9967
During effective range of
measurement
450 (42.3)
7475
X 100 Cal
150 (14.1)
2492
X 100 Ref
45 (4.23)
748
X 10 Cal
30 (2.28)
498
X 10 Ref
4.5 (0.42)
75
X 1 Cal
1.5 (0.14)
25
X 1 Ref
Note: Be sure to account for background reading when performing calibration. To calculate calibration constants:
(Expected Reading/ Net Reading) * Existing Calibration Constant = New Calibration Constant.
c.
The calibration software contains a calibration wizard to ease calibration. See the Model 3100
calibration software manual for more detailed instructions.
d.
Repeat calibration steps for the remaining range multipliers, or if doing a single point calibration, copy
the calibration constant found to the other two ranges.
A.4 FINAL CALIBRATION STEPS.
If the
137
Cs range calibration method was used to calibrate the tritium
reading, turn off the instrument and replace the +HV gamma bias battery, making sure to insert it into the holder
correctly. Close the instrument and turn it back ON. Verify that the +HV measurement in the check screen has a
check-mark beside it. Wait a minimum of four hours settling time to continue.
Gamma
Source
Gamma
Dimple
Tritium
Dimple
Содержание 3100
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