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

Abstract

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 ¹³²I to the exposure dose to residents was discussed from the measured values. The highest values of the ¹³¹I/ ¹³⁷Cs 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 ¹³²I/ ¹³¹I activity ratio in the same environmental samples had the lowest values, ranging from 0.01 to 0.02. By assuming that the ¹³²I/ ¹³¹I activity ratio in the atmosphere was equal to the ratio in the environmental samples, the percent contribution to the thyroid equivalent dose by ¹³²I was estimated to be less than 2%. Moreover, the contribution to the thyroid exposure by ¹³²I might be negligible if ¹³²I contamination was restricted to Iwaki City.