External doses to the public from contaminated land

Satoh, Daiki   

A database of conversion coefficients to convert the activity concentration to the effective dose rate for various ages that represent general population has been constructed for external exposure to radioactive cesium distributed in the soil, and the relationships between the personal dose equivalent rate, ambient dose equivalent rate, and effective dose rate have been analyzed. The age-dependent conversion coefficients were calculated for planar sources of radioactive cesium at source depth of 0.0, 0.5, 2.5, 5.0, 10.0 and 50.0 g/cm in the soil by incorporating the ICRP reference phantoms for newborns; 1-, 5-, 10-, and 15-year-old children; and adults into the Particle and Heavy Ion Transport Code System (PHITS), which is a Monte-Carlo simulation package. The definition of the effective dose given in the ICRP 2007 Recommendations was applied to the dose estimation not only for adults but also for children and babies here. The personal dose equivalent rate monitored by a personal dosimeter worn on the bodies of the public and the ambient dose equivalent rate were calculated in the same environmental radiation fields, and were compared with the effective dose rates. From the results, it was found that the personal dose equivalent provides a good estimate regarding the effective dose in a contaminated environment and does not exceed the ambient dose equivalent value at a height of 100 cm above the ground, while the effective doses for younger people are higher than those for adults. This means that the radiation exposure of the public in Fukushima can be controlled adequately by monitoring the personal dose equivalent using a dosimeter.