Activity concentrations of environmental samples collected in Fukushima Prefecture immediately after the Fukushima nuclear accident

Radionuclide concentrations in environmental samples such as surface soils, plants and water were evaluated by high purity germanium detector measurements. The contribution rate of short half-life radionuclides such as I-132 to the exposure dose to residents was discussed from the measured values. The highest values of the I-131/Cs-137 activity ratio ranged from 49 to 70 in the environmental samples collected at Iwaki City which is located to the south of the F1-NPS. On the other hand, the I-132/I-131 activity ratio in the same environmental samples had the lowest values, ranging from 0.01 to 0.02. By assuming that the I-132/I-131 activity ratio in the atmosphere was equal to the ratio in the environmental samples, the percent contribution to the thyroid equivalent dose by I-132 was estimated to be less than 2%. Moreover, the contribution to the thyroid exposure by I-132 might be negligible if I-132 contamination was restricted to Iwaki City.