Radiation Protection Bureau of Health Canada, 775 Brookfield Road, Ottawa, ON, K1A 1C1, Canada.
Ionizing Radiation Standards, National Research Council, Ottawa, ON, K1A 0R6, Canada.
J Environ Radioact. 2022 Nov;253-254:107009. doi: 10.1016/j.jenvrad.2022.107009. Epub 2022 Sep 10.
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 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.
自 2002 年以来，加拿大卫生部的固定点监测网络一直在监测加拿大的环境辐射暴露情况。该网络由 80 多个 7.6cm×7.6cm 的碘化钠光谱仪组成，定期向公众报告加拿大各地的环境伽马辐射水平。本文介绍了未来升级网络的空气比释动能和环境剂量当量的最新剂量校准。校准曲线是使用蒙特卡罗技术开发的，并通过在各种参考场中的实验进一步优化。在实验室条件下，对宽范围的伽马能量、剂量测量范围和入射角进行了剂量校准验证。在环境监测情况下，通过假设放射性羽流、地面污染和土壤源的相应暴露场景中的半无限羽流源、半无限平面源和无限体积源，对辐射暴露的角度分布进行了分析计算。通过将所得的辐射角度分布与探测器在剂量响应上的角度变化相结合，估计了这些环境场景中每个场景的剂量测量的整体准确性。预计羽流辐射的测量精度在±3.7%以内，Cs 地面污染的测量精度在-5.6%以内，土壤放射性源的测量精度在 0%至-17.1%以内。对土壤源的低估主要是由于晶体下方电子系统对辐射的吸收造成的。
