Dose Reconstruction for Heavily Exposed Patients of the Criticality Accident in Tokai-mura

A dose reconstruction for the heavily exposed patients is in progress using a numerical simulation technique where Monte Carlo simulation is applied under a calculation system that consists of the precipitation tank and two mathematical phantoms with movable arms and legs whose positions and postures are carefully modelled after those of patients A and B at the exposure. Tentative results show: (1) the average whole body neutron dose agreed well to that estimated by the measured specific activity of Na-24; (2) the average whole body gamma-ray dose was 2.4 times higher than the neutron dose for patient A and 1.9 times for patient B; (3) the highest dose at the skin of the abdomen for patient A was five times higher than the average whole body dose for neutrons and three times higher for gamma-rays; (4) the neutron dose in the body decreased markedly with a half value thickness of about 4 cm; (5) the contribution of neutron to the total dose reduced to 30% at 6 cm in depth, 25% at 10 cm and less than 10% at the back of the body