Calibration and Statistical Performance of Al2O3: C Optically Stimulated Luminescent Dosimeters With and Without Annealing Using a 137Cs Source.

A series of experiments were conducted using commercially available Al2O3:C optically stimulated luminescent dosimeters to provide a technical basis for their precise calibration and statistical performance at irradiated air kerma doses between 0.02 mGy and 5 mGy using Cs. This study examines the dose response linearity, studies the background signal for annealed dosimeters, and compares the statistical performance of dosimeters that were annealed and not annealed prior to their irradiation and readout. The average and standard deviation for the response of groups of dosimeters annealed and nonannealed prior to their irradiation were determined at each delivered dose. The batch of dosimeters that were annealed prior to their irradiation exhibited a coefficient of variation in its mean dose response below 10% when using three or more irradiation trials at each delivered air kerma dose between 0.02 mGy and 5 mGy. The reader calibration factor was calculated using the response of the annealed batch of dosimeters and was determined to be 756 ± 7 photomultiplier tube counts per mGy. Best estimates of the individual sensitivity factors were determined to be between 0.79 and 1.12 for the annealed batch of dosimeters. The minimum number of irradiations required to accurately determine the sensitivity factor of each individual dosimeter is reported with the recommended reader and dosimeter calibration procedures.

Setup and Characterization of a 137CS Dosimetry Calibration Source in a Space-constrained Environment.

Proper characterization of Cs sources used for dosimeter calibration and performance testing is crucial for accurate and precise knowledge of air kerma rate and delivered dose. A 269 GBq Cs source was relocated to a new facility, which had a footprint of approximately 2.8 m × 3.6 m and a 3.4 m high ceiling. A small room size, such as in the new facility, may significantly increase backscatter from the walls or room return. Due to the limited source strength, a relatively close irradiation position of 1.00 m from the source was selected to decrease required exposure times. Proximity to the small but cylindrical source has the potential to alter the 1/r relationship (inverse square law) of air kerma rate with distance associated with point sources. Practical tutorials concerning dosimetry irradiation facilities are largely absent from the archival literature. For those reasons, standard characterization experiments were repeated multiple times, great care was taken with positioning, several experiments were added to the standard ones, an ion chamber and dosimeters were used rather than film for greater accuracy and precision, and practical details of the process were recorded. The impacts of room size and finite source dimensions were quantified and mitigated by the efforts reported here. Recommendations for simple but thorough facility characterization, beam calibration, and quality control resulted.