Abstract In the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, a considerable amount of radioactive materials were released into the environment. Long-term monitoring is essential for radiation protection and decontamination of the environment. In this study, we analyze the ratio of the air dose rate to 137Cs activity per unit area on the ground over different land use types, and further examine the factors that influence this ratio. It was found that the ratio was relatively higher for forest areas than that for open areas, which may have been caused by effect of continuous 137Cs influx from the forest canopy for a while after the accident. The less influence of vertical migration to the ratio was shown, maybe because the soil shielding effect is negligible by considering more than 75% of 137Cs is still in the surface soil. The ratio is expected to be relatively less changeable in the future, owing to the immobilization of 137Cs in the soil after seven years. The ratio data can be used to estimate future air dose rates, based on the 137Cs activity per unit area for long-term monitoring and evaluation of decontamination activities.

中文翻译：

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核事故后 7 年不同土地用途单位面积空气剂量率与 137Cs 活度之比 - 福岛小木水库斜坡集水区案例 -

摘要 在福岛第一核电站（FDNPP）事故中，大量放射性物质被释放到环境中。长期监测对于辐射防护和环境净化至关重要。在本研究中，我们分析了不同土地利用类型的地面单位面积空气剂量率与 137Cs 活性的比率，并进一步研究了影响该比率的因素。研究发现，森林地区的比例相对高于开阔地区，这可能是由于事故发生后一段时间内137Cs从森林冠层持续流入的影响所致。显示出垂直迁移对比率的影响较小，可能是因为考虑到 75% 以上的 137Cs 仍在表层土壤中，土壤屏蔽效应可以忽略不计。由于 137C 在 7 年后固定在土壤中，预计该比率在未来的变化相对较小。该比率数据可用于估计未来的空气剂量率，基于单位面积的 137Cs 活动，用于长期监测和评估去污活动。