Early in situ measurement of radioactive fallout in Fukushima city due to Fukushima Daiichi nuclear accident

Using a high-purity germanium detector, both indoor and outdoor radionuclides that had deposited 1.5 d after the radioactive fallout events in the city of Fukushimawere experimentally measured. Eleven artificial (I-131, I-132, Cs-134, Cs-136, Cs-137, Te-129, Te-129m, Te-131m, Te-132, La-140 and Tc-99m) and 5 natural radionuclides were identified. Total air kerma rates were mainly due to I-132, Cs-134 and Cs-136 from 4 to 6 Gy/h at a 7.5-cm height from the ground. Radioactive contamination on the ground was contributed by I-132 and Te-132, from 330 to 420 Bq/cm(2). In a worst-case scenario, the maximum skin dose rates were estimated to be from 520 to 670 Gy/h. Effective dose rates were evaluated to be 10 to 15 Sv/h and reached 17.9 Sv/h at 4 a.m. on 16 March. In the effective dose rates, I-132, Cs-134 and Te-132 were the main contributors. Our measurements are useful for estimating dose levels in the public in the city of Fukushima during the days after radioactive fallout contamination.