Directional distribution of radiation around an accident at a uranium fuelfactory in Tokai-mura, 1999

A beta-ray survey was carried out on concrete walls of the boundary and bui ldings after a criticality accident at a factory of JCO Co. Ltd. at Tokai-m ura. A remarkable distribution of beta counts was observed on the walls dep ending on the complex internal and external structures of buildings surroun ding a precipitation vessel containing uranium 23 days after the accident. The directional distribution function, based on the beta counts on the wall s, aias consistent with data concerning the neutron dose rate measured in s everal directions during the accident, suggesting an anisotropic neutron di stribution to the residential area.