Airborne radiation survey after the accident

Torii, Tatsuo*  ; Sanada, Yukihisa   

Airborne radiation survey was conducted to evaluate the influence of radionuclides emitted by the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident. Carrying out airborne radiation surveys using a manned helicopter, the Japan Atomic Energy Agency (JAEA) has developed and established an analysis method concurrently with the development of this survey method. In particular, because the background radiation level differs greatly between the East and West regions of Japan, the JAEA has developed a discrimination method for natural radionuclide and cosmic rays using the gamma energy spectra. The reliability of the airborne radiation monitoring data was confirmed through comparison with large amounts of ground measurement data. Here, we report on the measurement technique and the results. The ambient dose rate has been decreased by the increasing attenuation effect due to radioactive cesium penetration into the soil in addition to the physical decay of radioactive cesium. These results indicate the importance of airborne monitoring to evaluate and predict the radiation exposure of residents.