GE RSDetection RS-S131-200-ER0000, Руководство пользователя

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RSDetection
User’s Manual
March 2016 S131-200-UM Rev A
Page 50
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6 C
ALIBRATION
Calibration is accomplished by placing the RSDetection in a well-defined radiation field and
adjusting calibration constants to produce a prescribed output. The exact details of a user’s
calibration procedure depend upon the equipment and resources available as well as the user
requirements.
It is recommended to implement a rapid method of checking sensor calibration. The intent is to
identify substantial changes in instrument calibration. The check consists of establishing a
reproducible arrangement of a long half-life isotopic source (e.g. Cs137) and the installed sensor.
The increase in the sensor indication above background due to the check source is proportional to
the sensitivity of the sensor. Any change in this indication is evidence of a change in calibration.
To perform this check:
1. Calculate an average value for background by averaging readings over a five-minute time
period.
2. Place the check source in a reproducible location corresponding to the center of the
chamber.
3. Average the readings for approximately two minutes.
4. Subtract the background value from the check source value to obtain the increase due to
the source. This value should be constant if the calibration does not change. This method
should be reproducible to within about 1% if carefully performed.
6.1 S
COPE
The following calibration procedure tests the sensor in the low range and identifies if the RAC
parameter of the system should be adjusted.
OBSERVE RADIATION SAFETY PRACTICES WHEN WORKING WITH A RADIOACTIVE
SOURCE. DUE TO THE WEIGHT OF THE LEAD SHIELD, MAKE SURE THAT THE STAND
HOLDING THE SOURCE IS STABLE.
This procedure uses a “shadow shield” method using a Cs137 source. It includes instructions for
averaging readings made at different field strengths, calculating instrument sensitivity in amps (A)
per roentgen (R) per hour, and converting that figure to sensitivity relative to a Ra226 spectrum.
A procedure is included for adjusting the sensitivity parameter of the system, if required, to bring
the instrument into specified tolerance. The number of measurements taken and the distances
used are determined by the calibration system designers. The sample calculations show
measurements taken at 12, 14, 16, and 18 feet.