title: 228Ra/226Ra ratio and 7Be concentration in the Sea of Japan as indicators for water transport: comparison with migration pattern of Fukushima Dai-ichi NPP-derived 134Cs and 137Cs.
abstract: To assess the migration patterns of radiocesium emitted from the Fukushima Dai-ichi Nuclear Power Plant (FDNPP), we analyzed (228)Ra/(226)Ra ratios and (7)Be concentrations and compared them with (134)Cs and (137)Cs concentrations in seawater samples collected within the Sea of Japan before and after the FDNPP accident (i.e., during the period 2007-2012) using low-background γ-spectrometry. The (228)Ra/(226)Ra ratios in surface waters exhibited lateral and seasonal variations, reflecting the flow patterns of surface water. This indicates the transport patterns of the FDNPP-derived radiocesium by surface water. Cosmogenic (7)Be (half-life: 53.3 d) exhibited markedly high concentrations (5-10 mBq/L) at depths shallower than 50 m, with concentrations decreasing steeply (0.2-2 mBq/L) at depths of 50-250 m. The distribution of (7)Be concentrations suggests that the downward delivery of the FDNPP-derived radiocesium to below 50 m depth was negligible for a few months prior to its removal from the Sea of Japan.
authors.affiliation: Low Level Radioactivity Laboratory, Institute of Nature and Environmental Technology, Kanazawa University, Nomi, Ishikawa 923-1224, Japan. Electronic address: mutsuo@llrl.ku-unet.ocn.ne.jp.
authors.forename: M
authors.initials: M
authors.lastname: Inoue
authors.forename: Y
authors.initials: Y
authors.lastname: Furusawa
authors.forename: K
authors.initials: K
authors.lastname: Fujimoto
authors.forename: M
authors.initials: M
authors.lastname: Minakawa
authors.forename: H
authors.initials: H
authors.lastname: Kofuji
authors.forename: S
authors.initials: S
authors.lastname: Nagao
authors.forename: M
authors.initials: M
authors.lastname: Yamamoto
authors.forename: Y
authors.initials: Y
authors.lastname: Hamajima
authors.forename: K
authors.initials: K
authors.lastname: Yoshida
authors.forename: Y
authors.initials: Y
authors.lastname: Nakano
authors.forename: K
authors.initials: K
authors.lastname: Hayakawa
authors.forename: S
authors.initials: S
authors.lastname: Oikawa
authors.forename: J
authors.initials: J
authors.lastname: Misonoo
authors.forename: Y
authors.initials: Y
authors.lastname: Isoda
mesh_terms: D001608:Beryllium / Q000032:analysis*; D002588:Cesium Radioisotopes / Q000032:analysis*; D062406:Fukushima Nuclear Accident; D007564:Japan; D011834:Radiation Monitoring; D011883:Radium / Q000032:analysis*; D012623:Seawater / Q000032:analysis*; D014872:Water Movements; D014875:Water Pollutants, Radioactive / Q000032:analysis*
chemical_list: D002588:Cesium Radioisotopes; D014875:Water Pollutants, Radioactive; D001608:Beryllium; D011883:Radium
keywords: (134)Cs; (228)Ra/(226)Ra ratio; (7)Be; Current profiles; Fukushima Dai-ichi Nuclear Power Plant accident; Sea of Japan