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

Mapes, Jasmine L.; Liu, Kevin; Abraham, Sara A.; Wilhelm, Andrew S.; Latosz, Logan V.; Kearfott, Kimberlee J.1

doi: 10.1097/HP.0000000000000941

Proper characterization of 137Cs 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 137Cs 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 2 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.

1University of Michigan, Department of Nuclear Engineering and Radiological Sciences, Ann Arbor, MI 48109‐2104.

The authors declare no conflicts of interest.

For correspondence contact: Kimberlee J. Kearfott, Department of Nuclear Engineering and Radiological Sciences, University of Michigan, 2355 Bonisteel Boulevard, Ann Arbor, MI 48109‐2104.

(Manuscript accepted 26 June 2018)

Jasmine Mapes is currently working towards her bachelor’s degree in Nuclear Engineering from the University of Michigan. She is a research assistant for the Radiological Health Engineering Laboratory. She hopes to continue on to graduate studies in nuclear engineering with a focus on detection and measurement research.

© 2018 by the Health Physics Society