Retrospective Estimation of the Spatial Dose Distribution and the Number of Fissions in Criticality Accident Using Area Dosimeters

A practical method is proposed for retrospective estimation of the spatial dose distribution and the number of fissions in a typical criticality accident where there is a single radiation source in an accessible room. In this method, two kinds of low-fading and tissue-equivalent dosimeters are used as area dosimeters: an alanine dosimeter and a thermoluminescence dosimeter made of enriched lithium tetra borate (Li-7(2) (B4O7)-B-11). The procedure of the method consists of four parts: (1) dosimetry using area dosimeters (2) search for the center of the radiation source, (3) estimation of the spatial dose distribution in the room, and (4) estimation of the number of fissions in the accident. Dosimetry of criticality accident situations simulated at the TRACY facility demonstrates the practicability of the method. Although a post-hoc analysis in principle, this method gives useful information on the magnitude and hazard level of the accident to determine the strategy of radiation emergency medicine and other post-accident measures if the area dosimeters are retrieved immediately after the accident.