Personnel working in areas where they may encounter radiation should be provided with portable survey meters to allow them to assess the dose rate, and they should also have devices that will record the total dose that they receive.
A variety of survey meters are available at the Reactor Facility which cover ranges from background to intense radiation fields. The instruments available are of different design: some are sensitive to alpha, beta, and gamma radiation, while others only register beta and gamma. Of these, some can differentiate between components. Neutron contributions may also be monitored using a special portable monitor.
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Survey meters generally indicate the radiation field in terms of the exposure dose rate (millirem per hour, or mR/h). They should be calibrated regularly to verify performance. Each monitor is usually equipped with a check source to be used to verify that the instrument is in good working order.
Direct reading pocket dosimeters are available at the Facility and should be worn by students whenever they are in the laboratory. This type of monitoring device integrates the dose rate received from beta and gamma radiation over time and thus provides an ongoing evaluation of the total exposure (mR) while in the Facility. Note that some indirect reading dosimeters are available, as are some which are neutron-sensitive. In addition, some have the ability to emit a signal when a pre-determined dose has been registered. This feature provides an obvious benefit to the user, but even with these units, visual examination of the accumulated dose is prudent.
Other instruments generally used for radiation survey work indicate the instantaneous dose rate seen by the sensitive volume of the detector, giving the user an immediate indication of his or her environment.
To acquaint the student with the use of dosimeters in the laboratory, and the concept of instrument calibration.
Clip the group of direct reading pocket dosimeters around the calibration ring after charging each and recording the initial, near-zero reading vs. serial number. Set the ring away from all structure.
Using the source calibration data, calculate the dose rate at the ring for the source which will be used. Determine the exposure time that must be used to achieve a mid-range reading on the dosimeter. Install the source on the central rod, rope off the area, and wait until the exposure time has elapsed. Remove the source, store properly in its shielded container, then record the final readings on the dosimeter.
To use and calibrate portable survey meters.
Select one of the Facility's portable survey meters, choose the suitable operating scale for measuring the dose rate at the ring used in Part I.
Using the portable survey meter, take a reading with the "front" of the sensitive volume at the ring. Take other readings with "center" and the "rear" of the sensitive volume at the ring. Repeat for other types of survey meters.
