Environmental and Radiological Health Sciences Faculty, Colorado State University, Fort Collins, CO.
Institute of Environmental Radioactivity, Fukushima University, Fukushima, Kanayagawa, Japan.
Health Phys. 2020 Jan;118(1):60-64. doi: 10.1097/HP.0000000000001129.
On 11 March 2011, a 9.0 magnitude earthquake struck the Tohoku region of Japan. The earthquake caused a 15 m tsunami that bombarded the east coast of the island nation. Among the losses was the damage to the Fukushima Daiichi nuclear reactor that lost onsite power and was unable to cool the reactor cores. The reactors melted down and released a plume of radionuclides into the environment. Radiocesiums (Cs and Cs) are the long-lived radionuclides of concern that were deposited along the plume and were distributed on the soil. Radiological decay models are typically used to determine the reduction in external radiation dose over time. However, these radiological decay models do not take into account physical removal by wind and water erosion, or sedimentation in soil outside expected depths. Thirty-five fixed dose-rate monitors were used to record dose rates at 1 mo intervals from the time of installation in Fukushima Prefecture in April 2012 until December 2018 and were used to estimate the effective half-life for radiocesium contamination based on external radiation dose rates. The effective half-life of cesium in the environment was calculated to be 3.2 ± 0.5 y, compared to a theoretical half-life of 7.8 y.
2011 年 3 月 11 日，日本东北地区发生了 9.0 级地震。地震引发了高达 15 米的海啸，袭击了这个岛国的东海岸。损失包括福岛第一核电站反应堆的损坏，该反应堆失去了现场电源，无法冷却反应堆堆芯。反应堆熔毁，并向环境中释放了一团放射性核素。放射性铯（Cs 和 Cs）是人们关注的长寿命放射性核素，它们沉积在羽流中，并分布在土壤中。放射性衰变模型通常用于确定随时间推移外部辐射剂量的减少。然而，这些放射性衰变模型没有考虑到风、水侵蚀的物理去除作用，或超出预期深度的土壤中的沉积作用。从 2012 年 4 月在福岛县安装开始，每隔 1 个月使用 35 个固定剂量率监测器记录剂量率，直到 2018 年 12 月，并用于根据外部辐射剂量率估计放射性铯污染的有效半衰期。环境中铯的有效半衰期计算为 3.2±0.5 年，而理论半衰期为 7.8 年。
