Simulation study of personal dose equivalent for external exposure to radioactive cesium distributed in soil
The personal dose equivalent was calculated for the public (newborns; 1-, 5-, 10-, and 15-year-old children; and adults) in an environment contaminated with radioactive cesium (134Cs and 137Cs) distributed in a soil at specific depths of 0.0, 0.5, 2.5, 5.0, 10.0, and 50.0 g/cm2, and the conversion coefficients for converting activity concentration to personal dose equivalent rate were provided for each age group. Monte Carlo calculations were performed using pediatric and adult computational phantoms incorporated into a particle and heavy ion transport code system. Compared with the effective dose and ambient dose equivalent at a height of 100 cm above the ground, the personal dose equivalent was found to provide a good estimate as a measurable quantity for the effective dose and did not exceed the ambient dose equivalent even in the environmental radiation fields, while the personal dose equivalent values increased for younger subjects. The weighted-integral method to obtain the personal dose equivalent for a volumetric source was applied to the analysis of exponential radioactive cesium distributions in the soil observed in Fukushima, and the calculation results successfully reproduced the measured data.
