Characterization of the energy response and backscatter contribution for two electronic personal dosimeter models

摘要

We characterized the energy response of personal dose equivalent ( H p ( 10 ) in mrem) and the contribution of backscatter to the readings of two electronic personal dosimeter (EPD) models with radionuclides commonly used in a nuclear medicine clinic. The EPD models characterized were the RADOS RAD-60R, and the SAIC PD-10i. The experimental setup and calculation of EPD energy response was based on ANSI/HPS N13.11-2009. Fifteen RAD-60R and 2 PD-10i units were irradiated using 99 m Tc , 131 I , and 131 I radionuclides with emission energies at 140 keV, 364 keV, and 511 keV, respectively. At each energy, the EPDs output in H p ( 10 ) [mrem] were recorded with 15 inch thick PMMA to simulate backscatter form the torso. Simultaneous free-in-air exposure rate measurements were also performed using two Victoreen ionization survey meters to calculate the expected EPD H p ( 10 ) values per ANSI/HPS N13.11-2009. The energy response was calculated by taking the ratio of the EPD H p ( 10 ) readings with the expected H p ( 10 ) readings and a two-tailed z -test was used to determine the significance of the ratio deviating away from unity. The contribution from backscatter was calculated by taking the ratio of the EPD H p ( 10 ) readings with and without backscatter material. A paired, two-tailed t -test was used to determine the significance of change in EPD H p ( 10 ) readings. The RAD-60R mean energy response at 140 keV was 0.85, and agreed to within 5% and 11% at 364 and 511 keV, respectively. The PD-10i mean energy response at 140 keV was 1.20, and agreed to within 5% at 364 and 511 keV, respectively. On average, in the presence of acrylic, RAD-60R values increased by 32%, 12%, and 14%, at 140, 364, and 511 keV, respectively; all increases were statistically significant. The PD-10i increased by 25%, 19%, and 10% at 140 keV, 364 keV, and 511 keV, respectively; however, only the 140 keV measurement was statistically significant. Although both EPD models performed within the manufacturers' specifications of ± 25 % in the energy ranges used, they fell outside of our criteria of 10% at lower energies, suggesting the need to calculate energy-dependent correction factors, depending on the intended EPD use.PACS numbers: 87.53.Bn, 87.55.N-, 87.57.U-