Investigations on radioactive substances released from the Fukushima Daiichi nuclear power plant

The Great East Japan Earthquake on March 11th, 2011, severely damaged the Fukushima Daiichi Nuclear Power Plant resulting in the diffusion of many radioactive substances throughout Fukushima prefecture. To examine these substances, we have carried out investigations for several months since immediately after the accident. We revealed that environmental high-level radiation spread northwesterly from the nuclear plant and several areas in Nakadori, the region located in the central part of the prefecture between Hamadori (east part of the prefecture) and Aizu-chihou (west part), was contaminated with mid-level radiation. We also analyzed radionuclides in soil and estimated future radiation levels.The importance of topsoil removal for decontamination has become an obvious countermeasure since many radioactive substances have settled on the surface. In addition, we investigated residential areas and their surroundings to find where high-level doses were likely to be detected for lowering the risk of exposure among residents.When little information was available, the investigations were implemented and the results contributed to both administrative policies and civil life.