[M-AG38_2AM2] 福島原発事故により放出された放射性核種の環境動態

[MAG38-10] 森林環境中の放射性セシウムの移行と林床の空間線量率の経時変化

*加藤 弘亮¹、恩田 裕一¹、ロフレド ニコラ¹、久留 景吾²、河守 歩³ (1.筑波大学アイソトープ環境動態研究センター、2.アジア航測株式会社、3.筑波大学大学院環境科学研究科)

キーワード：福島第一原子力発電所事故, セシウム137, 森林環境, 樹冠遮断, 移行, 空間線量率

We investigated the transfer of canopy-intercepted radiocesium to the forest floor following the Fukushima Daiichi nuclear power plant accident. The cesium-137 (Cs-137) contents of throughfall, stemflow, and litterfall were monitored in two coniferous stands (plantation of Japanese cedar) and a deciduous broad-leaved forest stand (beech with red pine). We also measured an ambient dose rate at different height in the forest by using a survey meter (TCS-172B, Hitachi-Aloka Medical, LTD.) and a portable Ge gamma-ray detector (Detective-DX-100T, Ortec, Ametek, Inc.). In decreasing order of total Cs-137 deposition from the canopy to forest floor were the mature cedar stand, the young cedar stand, and the broad-leaved forest. The ambient dose rate in forest exhibited height dependency and its vertical distribution varied by forest type and stand age. The ambient dose rate showed an exponential decrease with time for all the forest sites, however the decreasing trend differed depending on the height of dose measurement and forest type. The ambient dose rates at the canopy (approx. 10 m-) decreased earlier than physical attenuation of radiocesium, whereas those at the forest floor varied among three forest stands. These data suggested that an ambient dose rate in forest environment can be variable in spatially and temporally reflecting the transfer of radiocesium from canopy to forest floor.