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Instrument Calibrations and Testing - doe-std-1128-98_ch10071
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DOE Standard Guide of Good Practices for Occupational Radiological Protection In Plutonium Facilities
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Radiation Safety Training - doe-std-1128-98_ch10073


DOE-STD-1128-98
The calibration of photon monitoring instruments over the energy range from a few
keV to 300 keV is best accomplished with an x-ray machine and appropriate filters
that provide known x-ray spectra from a few kiloelectron volts to approximately
300 keV. Radionuclide sources should be used for higher energies. Most ion
chambers used to measure photon radiations have a relatively flat energy response
above 80 to 100 keV; 137Cs or 60Co are typically used to calibrate these instruments.
These sources also may be used to calibrate Geiger-Mueller (GM) type detectors
used for dose rate measurements. It should be noted that some GM detectors (e.g.,
those with no energy compensation) can show a large energy dependence,
especially below approximately 200 keV. GM detectors should not be used if not
energy compensated.
The calibration of alpha-detection instruments normally should be performed with
239Pu, 241Am, or 230Th sources. Several sources of different activities should be used
to calibrate different ranges.
Whenever possible, beta detectors should be calibrated to the beta energies of
interest in the workplace. A natural or depleted uranium slab source can be used for
calibration of beta detectors when beta radiations in the workplace have energies
similar to the uranium. International Organization for Standardization beta sources
should be used for all other purposes: the energy dependence of beta detectors can
be tested using the calibration sources listed in the ISO Publication 1980 (1984);
these include 90Sr, 90Y, 204Tl, and 147Pm.
The calibration and testing of crucial monitoring systems are extremely important
to the overall radiation protection program but have often been neglected. Effluent
monitoring and sampling systems and remote area monitoring systems (RAMs)
should be given several tests. The radiological, environmental, and mechanical
characteristics of the instrumentation portion of the system should be fully
evaluated prior to its first use to ensure its compatibility with performance
requirements and facility operating conditions. The effluent sampling losses from
the sample probe to the collector/detector should be determined. This test should be
repeated at least annually and when a significant change in the sampling equipment
is made. The sample probe should be examined at least once a year to verify that its
design or performance has not been changed by corrosion. The recorder of the
sample flow rate should be calibrated when it is installed and annually thereafter.
The operability of the overall system should be completely tested once, with repeat
tests only after modification, repair, or maintenance. Operability checks should be
scheduled at least monthly and calibration performed at least annually.
The operation of criticality or other radiation alarm signal systems should be
checked periodically to ensure that the alarms are audible at all potentially
occupied locations. To prevent any desensitizing of staff, the staff should be aware
that the tests will be performed, and where possible, tests should be scheduled
during off-shift hours. Building systems should be tested semiannually and the
area-wide system should be tested at least annually. Any portion of the
detector/alarm system that is affected by the test should be reconfirmed for
operability after the test is completed (e.g., if a detector is disconnected and a
signal is injected at that point, the detector should be tested immediately after it has
been reconnected).
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