Answer to Question #377 Submitted to "Ask the Experts"

What is the radiation environment that is to be monitored?

• What is the typical dose rate in the radiation environment to be monitored?
• Is the radiation environment in an area where there are acceptable environmental conditions, i.e., appropriate temperature, humidity, chemicals, background radiation, etc.?

The answers to the above questions will determine what type of dosimeter needs to be worn, i.e., TLD or film dosimeter, and, the length of monitoring period. The most prevalent Minimal Reportable Dose (MRD) for both the TLD and film dosimeter is 10 mrem over the entire monitoring period. If the individual is in a low exposure area, the facility might consider a longer monitoring period. Film can generally be worn up to 3 months, if appropriate QA is provided by the processing facility, and, proper environmental controls are implemented, and, the Control dosimeter is returned with the personnel dosimeters. The only disadvantage I can state may be the potential false positives that may occur when the film is exposed at the MRD level, at approximately 10 mrem. If the dose determination is 9.5 mrem, there is no dose reported. But at 9.6 the dose reported would be 10 mrem. The statistics are poor at this low dose. A TLD on the other hand can be worn for up to 6 months when the dose is required to be measured by regulatory entities. For those who wish to be monitored, but are not required to be monitored by regulatory entities, the TLD can be worn for up to 12 months, without any appreciable dose degradation, as long as appropriate fade correction is implemented by the processing facility. There are significant advantages in wearing a film dosimeter in an x-ray environment: Film is an excellent x-ray spectra differentiator. With 4 or 5 filtered areas for dose assessment, the appropriate x-ray energy can be determined quite accurately. Film can be analyzed to determine whether or not the exposure was received during an occupational exposure, or, whether or not the film was irradiated in a stationary mode, where the person was not occupationally exposed. The film can be maintained indefinitely, and can be reassessed, or be used during litigation. A TLD, once read, can not be reprocessed. The only factor that can be reviewed is the TLD glow curve, which determines whether or not the TLD was damaged, or, that the dose reported is an accurate dose assessment. In conclusion, there are few disadvantages in using a film dosimeter in an x-ray environment. The reality is, it is probably the best dosimeter to be worn in an x-ray environment.

Sander C. Perle