Producing Traceable Irradiations for Calibration of Dosimeters or Instruments

Scott O. Schwahn
DOELAP Performance Evaluation Program Administrator
U.S. Department of Energy

The Department of Energy Laboratory Accreditation Program (DOELAP) operates an irradiation facility for testing dosimetry programs.  Sources of irradiations include gamma rays (Cs-137, Co-60, and Am-241), x rays (both NIST* and ISO** beam qualities), and beta particles (Tl-204, Sr/Y-90, and uranium slabs). While it is commonly understood that factors such as time and distance must be considered for known irradiation quantities, many more variables have to be understood and accounted for. For photon irradiations, those variables include temperature, pressure, humidity, room scatter, depth dose, beam quality, calibration, uniformity, and uncertainty. Each of these considerations must be addressed for irradiations to be considered "traceable." Also, an interesting phenomenon has been identified recently at DOELAP having to do with variations in phantom backscattering. These variations may have unanticipated consequences for the internationally accepted methodology for irradiating dosimeters.
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*NIST: National Institute of Standards and Technology
**ISO: International Organization for Standardization