Thermal neutron fluence from ultra low-level gamma-ray spectrometry of spoons activated during the JCO criticality accident at Tokai-mura in 1999.
During the JCO-accident in Tokai-mura in 1999, the surrounding village was irradiated by an uncontrolled neutron flux. At some locations in that village, the thermal neutron flux was determined retrospectively by measurement of the very low activity of 51Cr and 60Co in stainless-steel spoons using gamma-ray spectrometry in underground laboratories. Activities determined in the HADES underground facility are presented here, together with calibrations performed using a well-defined thermal neutron flux to directly estimate the fluence of thermal neutrons independent of most assumptions. The results show measurable 51Cr in three samples and 60Co in four samples taken from locations at distances of up to 430m from the accident location despite the elapse of 4 half-lives of 51Cr before measurement. Effects of air transport of the samples were considered and shown to be negligible.
Hult
Mikael
M
European Commission, Joint Research Centre, Institute for Reference Materials and Measurements, Geel, Belgium. mikael.hult@irmm.jrc.be
Martínez Canet
María Jose
MJ
Johnston
Peter N
PN
Komura
Kazuhisa
K
D000392:Air Movements; D002138:Calibration; D002860:Chromium Radioisotopes / Q000032:analysis; D003037:Cobalt Radioisotopes / Q000032:analysis; D004784:Environmental Monitoring / Q000379:methods*; D005720:Gamma Rays; D006207:Half-Life; D007564:Japan; D009502:Neutrons; D018788:Radioactive Hazard Release; D013053:Spectrophotometry / Q000379:methods
D002860:Chromium Radioisotopes; D003037:Cobalt Radioisotopes