Characterization of a 20 curie, cesium-137 irradiator

Abstract

The Department of Energy Laboratory Accreditation Program (DOELAP) located at the Radiological and Environmental Sciences Laboratory (RESL) at Idaho National Engineering and Environmental Laboratory is charged with evaluating and accrediting personnel dosimetry systems for a variety of research and engineering facilities nationwide. [] irradiating are used in DOELAP to deliver accident-and protection-level doses to personal dosimeters. It is absolutely paramount that the calibration radiation fiends are well characterized. During the summer of 1997, the DOELAP Calibration Laboratory Facility was remodeled to accommodate an increasing workload. Remodeling the laboratory facility and the installation of a new, automated control calibration system required a complete characterization of DOELAP'S 20 Ci [] beam, irradiated verify that the new DOELAP configuration was in compliance with the DOE Standard for Performance Testing of Personnel Dosimetry Systems. A rail mapping experiment determined that scatter from ancillary equipment and wails minimally affected exposure along the axis of the source beam, with the experimental exposure varying only 0.25% to 1% from the theoretical exposure. In addition, a new procedure was authored to provide guidelines for future DOELAP rail mapping experiments. To ensure that all dosimeters receive the same dose during DOELAP irradiations, beam uniformity measurements were also source using both an ionization chamber and a film exposure. Beam uniformity results, using an ion chamber, showed a pronounced penumbra at the edge of a whole body phantom at 100 centimeters. The beam was fairly uniform at 200 centimeters. Beam uniformity results the DOELAP dosimeter mounting area showed that the beam was uniform at both 100 and 200 centimeters with maximum deviation of approximately 1-1.5%. Comparing beam uniformity results between the ionization chamber and the film exposures determined that using film was an acceptable practice for determining beam uniformity and requires less time. As an extension of this experiment, a new internal procedure for verifying beam uniformity was authored for future DOELAP use. Factors that convert exposure to dose equivalent (Cx) for the 20 Ci, irradiated were within DOELAP standards (DOE 1986). Characterization the DOELAP 20 Ci, [] source has verified that the new DOELAP configuration is in compliance with the DOE Standard for Performance Testing of Personnel Dosimetry Systems.