IMPACT ON ABSORBED DOSE RATE IN AIR IN THE IZU ISLANDS FROM LONG HALF-LIFE RADIONUCLIDES RELEASED BY THE FUKUSHIMA DAIICHI NUCLEAR POWER PLANT ACCIDENT

摘要

Car-borne surveys were carried out on eight islands of the Izu Islands located 339-570 km southwest of the Fukushima Daiichi Nuclear Power Plant. The mean dose rates measured in 2015, 2016 or 2017 on each island were from 12 to 47 nGy h(-1), meaning that the contribution ratios of artificial radionuclides were 5-31%. Based on the environmental half-life for long half-life radionuclides (Cs-134 + Cs-137) measured on Izu-Oshima (3.1 y), the mean dose rates in March 2011 were estimated to be 15-53 nGy h(-1) and the contribution ratios of artificial radionuclides were 11-55%. The estimated annual external effective doses were 0.06-0.21mSv which were 13-44% of the worldwide average (0.48mSv).