title: External doses in the environment from the Tokai-mura criticality accident.
abstract: On 30 September 1999, a criticality accident occurred at a uranium processing plant operated by JCO in Tokai-mura, Japan and the criticality remained for about 20 h. Almost all doses to the neighbouring residents were brought by neutrons and gamma rays emitted from the facility rather than fission products released to the environment. External doses in the environment were evaluated using radiation monitoring data and radiation transport calculation. A pattern of the dose rate evolution was modelled based on the records of gamma ray monitors in the JCO facilities. Relations between the ambient dose equivalent rates of neutrons/gamma rays and the distance from the facility were determined from the monitoring data obtained around the accident site. Conversion from the ambient dose equivalent to the effective dose equivalent was made assuming the energy spectra calculated by the radiation transport code, ANISN. It was estimated that the people who stayed outside the 350 m zone would receive doses of less than 1 mSv.
authors.affiliation: Department of Health Physics, Japan Atomic Energy Research Institute, Tokai-mura, Ibaraki-ken 319-1195, Japan.
authors.forename: A
authors.initials: A
authors.lastname: Endo
authors.forename: Y
authors.initials: Y
authors.lastname: Yamaguchi
authors.forename: Y
authors.initials: Y
authors.lastname: Sakamoto
authors.forename: M
authors.initials: M
authors.lastname: Yoshizawa
authors.forename: S
authors.initials: S
authors.lastname: Tsuda
mesh_terms: D005720:Gamma Rays; D007564:Japan; D009502:Neutrons; D011834:Radiation Monitoring; D011847:Radioactive Fallout / Q000032:analysis*; D018788:Radioactive Hazard Release; D011874:Radiometry
chemical_list: D011847:Radioactive Fallout