Dose rate estimation for northern Miyagi prefecture area in the early stage of the Fukushima accident

Due to the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident, the Tohoku and northern Kanto areas were widely contaminated. Many soil contamination surveys around the Fukushima Prefecture and southern Miyagi Prefecture areas have been reported. However, there are few reports for the northern Miyagi Prefecture area. A moss sample was taken from Tome City on the 1^st May 2011 and measured with a Ge detector. Radioactive nuclides of ^129m,129Te, ¹³¹I, ^134,136,137Cs, ^110mAg, and ¹⁴⁰La were clearly identified in the moss sample. The identified radionuclides are the same as those from the FDNPP accident. In order to estimate the radiation dose rate in the northern Miyagi Prefecture area, soil sampling of 30 cm cores was performed at nine locations (Tome City, Kurihara City, Osaki City, Daiwa Town, Sanbongi Town, and Sendai City) on the 19^th August 2011. Radioactive concentrations in the soil samples were measured and obtained using a Ge detector. The minimum and maximum concentrations of the sum of the ¹³⁴Cs and ¹³⁷Cs radionuclides in the soil were found to be 2.76 and 35.2 kBq/m² for the Michino-eki in Sanbongi Town and the Izunuma Lake in Kurihara City, respectively. The radiation dose rate in the early stage of the FDNPP accident in the northern Miyagi prefecture has been estimated using radionuclide concentrations in moss and soil samples. The maximum dose rate at the sampling locations was estimated to be 1.8 μSv/h near the Izunuma Lake in Kurihara City on the 15^th March 2011. The cumulative dose for one year from the 15^th March 2011 was estimated to be 1.73-1.81 mSv by the fallout (1.2 mSv) and the natural background (0.53-0.61 mSv). (author)