Body surface contamination levels of residents under different evacuation scenarios after the Fukushima Daiichi Nuclear Power Plant Accident

Body surface contamination levels should be correlated with inhaled actual thyroid doses during evacuation following the Fukushima Daiichi nuclear power plant (FDNPP) accident. Evacuees and residents were screened for body surface contamination using a Geiger-Mueller survey meter. The authors obtained 7,539 individual screening data sheets as well as gamma-spectrometry data from measurements made on clothing of two subjects by using a germanium spectrometer. Body surface contamination levels were analyzed in four residential groups during two different periods: 12-14 and 15-17 March 2011. Contamination levels during 12-14 March in the Tomioka/Okuma/Futaba/Naraha group were very low, indicating that residents evacuated before the radioactive plume reached their towns on 12 March. In contrast, levels in the Namie and Minamisoma groups were higher than those in the other groups in both periods, indicating that these residents were exposed to plumes twice on 12 and 15-16 March. The plume on 12 March was enriched with short-lived radionuclides: Averaged proportions of radioactivity (relative to ¹³¹I) from ¹³²Te, ¹³³I, and ¹³⁷Cs measured in clothing from two subjects were 2.3, 1.1, and 0.1, respectively, after correction for physical decay by 12:00 on 12 March. These proportions are similar to those (relative to ¹³¹I) from ¹³²Te and ¹³⁷Cs in dust sampled by a high-volume air sampler in the zone 20 km from the FDNPP on 12 March: 1.9 and 0.1, respectively. These data indicate that the relative contribution to inhaled thyroid dose of short-lived radionuclides in radioactive plumes released on 12 March could be as much as 37.5% in 1-y-old children.