Early radiation survey of Iitate village, which was heavily contaminated by the Fukushima Daiichi accident, conducted on 28 and 29 March 2011

Abstract

Following the news that the radiation level in Iitate Village, located 25-45 km from the Fukushima Daiichi Nuclear Power Plant, was seriously increased, an urgent field survey was carried out on 28 and 29 March 2011. Radiation levels at 130 locations were measured inside a van that traveled throughout the village using a CsI pocket survey meter and an ionization chamber. Soil samples were also taken at five locations and submitted to gamma ray analysis using a Ge detector. A radiation exposure rate of more than 20 μSv h was observed in the southern part of Iitate Village. Volatile radionuclides such as iodine and cesium were found to be the main components of radioactive contamination. A trace amount of plutonium isotopes originating from the accident was also confirmed in several soil samples, the level of which was less than the global fallout. Based on the measured density of radionuclides at the highest contamination location during the present survey, an exposure rate of about 200 μGy h at 1 m above the ground was estimated at the time of the radioactive deposition on March 15. At this location, the cumulative exposure would reach 50 mGy in the middle of May 2011.