Widespread diffusion of radioactive materials and deposition on the ground surface; Radiation monitoring immediately after the Fukushima Daiichi Nuclear Power Plant accident and its fluctuations

Torii, Tatsuo*  ; Sanada, Yukihisa   

Ten years have passed since the accident at the Fukushima Daiichi Nuclear Power Station (FDNPS) caused by the Great East Japan Earthquake, and various efforts are being made in the field of radiation measurement. In an environment contaminated with radioactive material due to an accident, the contamination and air dose rate of radioactive material deposited on the ground surface can be monitored by various methods such as air, automobile, and human measurement. The Japan Atomic Energy Agency (JAEA) conducted an aerial radiation survey using a manned helicopter, and developed and established an analysis method at the same time as the development of this survey method. The reliability of the aerial radiation monitoring data was confirmed through comparison with a large amount of ground measurement data. In addition to the physical decay of radioactive cesium, the increased damping effect of the infiltration of radioactive cesium into the soil reduced the air dose rate. These results demonstrate the importance of aerial monitoring to assess and predict radiation exposure of residents.