Gamma survey in Fukushima prefecture right after the accident at Fukushima nuclear power plant (The 12th International Conference on Radiation Shielding (ICRS-12) and the 17th Topical Meeting of the Radiation Protection and Shielding Division of ANS (RPSD-2012)) -- (Accident of Fukushima Nuclear Power Plant and Its Influence)

On March 15-17 and April 8, 2011, right after the accident at Fukushima nuclear power plant, γ-ray dose-rate distributions and spectra were measured on expressways in Fukushima and neighboring prefectures using an NaI(Tl) dosimeter and a LaBr3 spectrometer. A radioactive plume was observed near Koriyama-city on 15. Although the distributions of Te, I, Cs, Cs, and Cs resembled each other, the distribution of I was different from the others. The dominant radionuclides of dose rate were Te and I on March 15-17 and Cs and Cs on April 8. The initial distribution profile of the dose rate on March 15-17 remained on April 8, which showed the deposited radioactive material was not moved from the initial location and there was no additional effective deposition of radioactivity after March 15.