Dose calibration of Health Canada's Fixed Point Surveillance system for environmental radiation monitoring in terms of air kerma and H*(10). (November 2022) - Liu, Chuanlei
Abstract: The environmental radiation exposure in Canada has been monitored since 2002 by Health Canada's Fixed Point Surveillance network. The network consists of over eighty 7.6 cm × 7.6 cm sodium iodide spectrometers, and routinely reports to the public the environmental gamma radiation level throughout Canada. This paper describes the latest dose calibrations to air kerma and ambient dose equivalent for the future upgraded network. The calibration curves were developed using Monte Carlo techniques and further optimized via experiments in various reference fields. The dose calibration was validated over a wide range of gamma energy, dose measurement range, and angle of incidence under laboratory conditions. In environmental monitoring situations, the angular distribution of radiation exposure was analytically calculated by assuming a semi-infinite plume source, semi-infinite planar source, and infinite volume sources for the respective exposure scenarios of radioactive plume, ground contamination, and soil source. By coupling the resultant radiation angular distribution with detector's angular variation on dose response, the overall accuracy of dose measurement in each of these environmental scenarios was estimated. The accuracy is expected to be within ±3.7% for plume radiation, −5.6% for 137 Cs ground contamination, and 0% to −17.1% for soil radioactive sources. The under-estimation for soil sources is mainly caused by absorption of radiation in the electronic system underneath the crystal. Highlights: The detectors of Health Canada's Fixed Point Surveillance network were calibrated to air kerma and ambient dose equivalent. Dose calibration was based on Monte Carlo method and validated with empirical data. The linearity, energy dependence and angular dependence of dose measurement were checked under laboratory conditions. The overall accuracy of dose measurement was estimated in a few environmental monitoring scenarios. The conformity of dose calibration to international standards on the dose response and accuracy was reviewed.