ABSTRACT Air dose rates within a range of 80 km from the Fukushima Dai-ichi Nuclear Power Plant measured via car-borne surveys using the KURAMA systems from 2011 to 2018 were analyzed. The ratio of the air dose rates relative to the first car-borne survey was 0.08 over a period of seven years, indicating a much more rapid decrease than that estimated by the physical decay of radiocesium (0.3). Differences in the decreasing trends of the air dose rates among the land-use categories and evacuation order areas were examined. The ecological half-lives were evaluated according to the land-use categories in each evacuation order area. To model the acceleration of the decrease in the air dose rates observed in the evacuation order area, we modified the bi-exponential curve formula of ecological half-life and introduced the two-group model. The ecological half-life of the fast components in the evacuation order area of ‘zone in preparation for the lifting of the evacuation order’ evaluated using the two-group model after 2013 were 0.5–1 y, which were much shorter than those before 2013 (2–3 y).

中文翻译：

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使用截至 2018 年由 KURAMA 系统测量的车载调查数据，评估福岛第一核电站 80 公里范围内空气剂量率和生态半衰期的下降趋势

摘要 分析了 2011 年至 2018 年使用 KURAMA 系统通过车载调查测量的福岛第一核电站 80 公里范围内的空气剂量率。在七年的时间里，空气剂量率相对于第一次车载调查的比率为 0.08，表明比放射性铯的物理衰变估计的下降速度 (0.3) 快得多。研究了土地利用类别和疏散命令区域之间空气剂量率下降趋势的差异。根据每个疏散命令区域的土地利用类别评估生态半衰期。为了模拟疏散命令区观察到的空气剂量率下降的加速，我们修改了生态半衰期的双指数曲线公式，并引入了两组模型。