title: The air dose rate around the Fukushima Dai-ichi Nuclear Power Plant: its spatial characteristics and temporal changes until December 2012.
abstract: Distribution maps of air dose rates around the Fukushima Dai-ichi Nuclear Power Plant were constructed using the results of measurement obtained from approximately 6500 locations (at most) per measurement period. The measurements were conducted 1 m above the ground using survey meters in flat and spatially open locations. Spatial distribution and temporal change of the air dose rate in the area were revealed by examining the resultant distribution maps. The observed reduction rate of the air dose rate over the 18 months between June 2011 and December 2012 was greater than that calculated from radioactive decay of radiocesium by 10% in relative percentage except decontaminated sites. This 10% difference in the reduction of the air dose rate can be explained by the mobility of radiocesium in the depth direction. In the region where the air dose rate was lower than 0.25 μSv h(-1) on June 2011, the reduction of the air dose rate was observed to be smaller than that of the other dose rate regions, and it was in fact smaller than the reduction rate caused by radioactive decay alone. In contrast, the reduction rate was larger in regions with higher air dose rates. In flat and spatially open locations, no significant difference in the reduction tendency of air dose rates was observed among different land use classifications (rice fields, farmland, forests, and building sites).
authors.affiliation: Fukushima Environmental Safety Center, Sector of Fukushima Research and Development, Japan Atomic Energy Agency, 2-2-2, Uchisaiwai-cho, Chiyoda, Tokyo 100-8577, Japan. Electronic address: mikami.satoshi@jaea.go.jp.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Mikami
authors.affiliation: General Analysis Division, Japan Chemical Analysis Center, 295-3, Sanno-cho, Inage, Chiba 263-0002, Japan. Electronic address: t-maeyama@jcac.or.jp.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Maeyama
authors.affiliation: Division of Emergency Preparedness Technology, Nuclear Safety Technology Center, 5-1-3-101, Hakusan, Bunkyo, Tokyo 112-8604, Japan. Electronic address: yoshi-hoshide@nustec.or.jp.
authors.forename: Yoshifumi
authors.initials: Y
authors.lastname: Hoshide
authors.affiliation: Institute of Radiation Measurements, 2-4 Shirane, Shirakata, Tokai-mura, Naka, Ibaraki 319-1106, Japan. Electronic address: r.sakamoto@irm.or.jp.
authors.forename: Ryuichi
authors.initials: R
authors.lastname: Sakamoto
authors.affiliation: Radioactive Analysis Division, Japan Chemical Analysis Center, 295-3, Sanno-cho, Inage, Chiba 263-0002, Japan. Electronic address: s-sato@jcac.or.jp.
authors.forename: Shoji
authors.initials: S
authors.lastname: Sato
authors.affiliation: Division of Emergency Preparedness Technology, Nuclear Safety Technology Center, 5-1-3-101, Hakusan, Bunkyo, Tokyo 112-8604, Japan. Electronic address: okuda@nustec.or.jp.
authors.forename: Naotoshi
authors.initials: N
authors.lastname: Okuda
authors.affiliation: Hitachi Solutions East Japan, Ltd., NBF Sendai Honcho Bldg, 2-16-10 Honcho, Aoba-ku, Sendai 980-0014, Japan. Electronic address: tetsuro.sato.aj@hitachi-solutions.com.
authors.forename: Tetsuro
authors.initials: T
authors.lastname: Sato
authors.affiliation: Center for Computational Science & e-Systems, Japan Atomic Energy Agency, 5-1-5, Kashiwanoha, Kashiwa, Chiba 277-8587, Japan. Electronic address: takemiya.hiroshi@jaea.go.jp.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Takemiya
authors.affiliation: Fukushima Environmental Safety Center, Sector of Fukushima Research and Development, Japan Atomic Energy Agency, 2-2-2, Uchisaiwai-cho, Chiyoda, Tokyo 100-8577, Japan. Electronic address: kimiaki.saito@jaea.go.jp.
authors.forename: Kimiaki
authors.initials: K
authors.lastname: Saito
mesh_terms: D062406:Fukushima Nuclear Accident; D062305:Geographic Mapping; D007564:Japan; D055848:Nuclear Power Plants; D011834:Radiation Monitoring; D011847:Radioactive Fallout / Q000032:analysis*; D011868:Radioisotopes / Q000032:analysis*; D012621:Seasons; D012990:Soil Pollutants, Radioactive / Q000032:analysis*
chemical_list: D011847:Radioactive Fallout; D011868:Radioisotopes; D012990:Soil Pollutants, Radioactive
keywords: Air dose rate; Distribution; Fukushima; Survey meter; Temporal change