title: Evaluation of ambient dose equivalent rates influenced by vertical and horizontal distribution of radioactive cesium in soil in Fukushima Prefecture.
abstract: The air dose rate in an environment contaminated with (134)Cs and (137)Cs depends on the amount, depth profile and horizontal distribution of these contaminants within the ground. This paper introduces and verifies a tool that models these variables and calculates ambient dose equivalent rates at 1 m above the ground. Good correlation is found between predicted dose rates and dose rates measured with survey meters in Fukushima Prefecture in areas contaminated with radiocesium from the Fukushima Dai-ichi Nuclear Power Plant accident. This finding is insensitive to the choice for modeling the activity depth distribution in the ground using activity measurements of collected soil layers, or by using exponential and hyperbolic secant fits to the measurement data. Better predictions are obtained by modeling the horizontal distribution of radioactive cesium across an area if multiple soil samples are available, as opposed to assuming a spatially homogeneous contamination distribution. Reductions seen in air dose rates above flat, undisturbed fields in Fukushima Prefecture are consistent with decrement by radioactive decay and downward migration of cesium into soil. Analysis of remediation strategies for farmland soils confirmed that topsoil removal and interchanging a topsoil layer with a subsoil layer result in similar reductions in the air dose rate. These two strategies are more effective than reverse tillage to invert and mix the topsoil.
authors.affiliation: Center for Computational Science & e-Systems, Japan Atomic Energy Agency, 178-4-4 Wakashiba, Kashiwa, Chiba, 277-0871, Japan. Electronic address: malins.alex@jaea.go.jp.
authors.forename: Alex
authors.initials: A
authors.lastname: Malins
authors.affiliation: Sector of Fukushima Research and Development, Japan Atomic Energy Agency, 1-29 Okitama-cho, Fukushima-shi, Fukushima, 960-8034, Japan; Sector of Decommissioning and Radioactive Wastes Management, Japan Atomic Energy Agency, 4-33 Muramatsu, Tokai-mura, Naka-gun, Ibaraki, 319-1194, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Kurikami
authors.affiliation: Sector of Fukushima Research and Development, Japan Atomic Energy Agency, 1-29 Okitama-cho, Fukushima-shi, Fukushima, 960-8034, Japan.
authors.forename: Shigeo
authors.initials: S
authors.lastname: Nakama
authors.affiliation: Sector of Fukushima Research and Development, Japan Atomic Energy Agency, 1-29 Okitama-cho, Fukushima-shi, Fukushima, 960-8034, Japan; Sector of Decommissioning and Radioactive Wastes Management, Japan Atomic Energy Agency, 4-33 Muramatsu, Tokai-mura, Naka-gun, Ibaraki, 319-1194, Japan.
authors.forename: Tatsuo
authors.initials: T
authors.lastname: Saito
authors.affiliation: Center for Computational Science & e-Systems, Japan Atomic Energy Agency, 178-4-4 Wakashiba, Kashiwa, Chiba, 277-0871, Japan.
authors.forename: Masahiko
authors.initials: M
authors.lastname: Okumura
authors.affiliation: Center for Computational Science & e-Systems, Japan Atomic Energy Agency, 178-4-4 Wakashiba, Kashiwa, Chiba, 277-0871, Japan.
authors.forename: Masahiko
authors.initials: M
authors.lastname: Machida
authors.affiliation: Sector of Fukushima Research and Development, Japan Atomic Energy Agency, 1-29 Okitama-cho, Fukushima-shi, Fukushima, 960-8034, Japan; Sector of Decommissioning and Radioactive Wastes Management, Japan Atomic Energy Agency, 4-33 Muramatsu, Tokai-mura, Naka-gun, Ibaraki, 319-1194, Japan.
authors.forename: Akihiro
authors.initials: A
authors.lastname: Kitamura
mesh_terms: D000396:Air Pollutants, Radioactive / Q000032:analysis; D002588:Cesium Radioisotopes / Q000032:analysis*; D062406:Fukushima Nuclear Accident; D007564:Japan; D011829:Radiation Dosage; D011834:Radiation Monitoring / Q000379:methods*; D011847:Radioactive Fallout / Q000032:analysis; D012990:Soil Pollutants, Radioactive / Q000032:analysis*
chemical_list: D000396:Air Pollutants, Radioactive; D002588:Cesium Radioisotopes; D011847:Radioactive Fallout; D012990:Soil Pollutants, Radioactive
keywords: Cesium profile in soil; Dose rate evaluation; Fukushima Dai-ichi NPP; PHITS; Soil remediation