Two-years trend of monthly 137Cs deposition observed in Kanto and south Tohoku areas, Japan: effects of the Fukushima Dai-ichi nuclear power plant accident

To elucidate deposition behavior of the FDNPP-derived radionuclides after the major emission in March 2011, two-years trends (March 2011 to April 2013) of the monthly Cs-137 deposition at monitoring stations of Kanto and south Tohoku regions were examined. The higher Cs-137 depositions within about 300 km of the FDNPP than pre-Fukushima level were still observed until April 2013. The monthly Cs-137 deposition showed marked winter peaks in 2012 and 2013 at the Futaba station, about 5 km of the FDNPP. The monthly Cs-137 deposition generally decreased with increasing distance from the FDNPP.