title: Differences in rates of decrease of environmental radiation dose rates by ground surface property in Fukushima City after the Fukushima Daiichi nuclear power plant accident.
abstract: After the Great East Japan Earthquake on 11 March 2011, the environmental radiation dose in Fukushima City increased. On 11 April, 1 mo after the earthquake, the environmental radiation dose rate at various surfaces in the same area differed greatly by surface property. Environmental radiation measurements continue in order to determine the estimated time to 50% reduction in environmental radiation dose rates by surface property in order to make suggestions for decontamination in Fukushima. The measurements were carried out from 11 April to 11 November 2011. Forty-eight (48) measurement points were selected, including four kinds of ground surface properties: grass (13), soil (5), artificial turf (7), and asphalt (23). Environmental radiation dose rate was measured at heights of 100 cm above the ground surface. Time to 50% reduction of environmental radiation dose rates was estimated for each ground surface property. Radiation dose rates on 11 November had decreased significantly compared with those on 11 April for all surface properties. Artificial turf showed the longest time to 50% reduction (544.32 d, standard error: 96.86), and soil showed the shortest (213.20 d, standard error: 35.88). The authors found the environmental radiation dose rate on artificial materials to have a longer 50% reduction time than that on natural materials. These results contribute to determining an order of priority for decontamination after nuclear disasters.
authors.affiliation: Department of Hygiene and Preventive Medicine, Fukushima Medical University School of Medicine, Fukushima, Japan. bamboo@fmu.ac.jp
authors.forename: Takeyasu
authors.initials: T
authors.lastname: Kakamu
authors.forename: Hideyuki
authors.initials: H
authors.lastname: Kanda
authors.forename: Masayoshi
authors.initials: M
authors.lastname: Tsuji
authors.forename: Daisuke
authors.initials: D
authors.lastname: Kobayashi
authors.forename: Masao
authors.initials: M
authors.lastname: Miyake
authors.forename: Takehito
authors.initials: T
authors.lastname: Hayakawa
authors.forename: Shin-ichiro
authors.initials: S
authors.lastname: Katsuda
authors.forename: Yayoi
authors.initials: Y
authors.lastname: Mori
authors.forename: Toshiyasu
authors.initials: T
authors.lastname: Okouchi
authors.forename: Akihiro
authors.initials: A
authors.lastname: Hazama
authors.forename: Tetsuhito
authors.initials: T
authors.lastname: Fukushima
mesh_terms: D055866:Earthquakes; D006801:Humans; D007564:Japan; D055848:Nuclear Power Plants; D011829:Radiation Dosage; D011834:Radiation Monitoring / Q000379:methods*; D018788:Radioactive Hazard Release