Application of topographical source model for air dose rates conversions in aerial radiation monitoring

Ishizaki, Azusa  ; Sanada, Yukihisa   ; Ishida, Mutsushi; Munakata, Masahiro 

After the Fukushima Daiichi Nuclear Power Station (FDNPS) accident in 2011, aerial radiation monitoring (ARM) using a manned helicopter was conducted to rapidly measure air dose rates and the deposition of radioactive nuclides over a large area. Typically, the air dose rate is obtained by conversion from the count rate using the conventional flat source model (FSM). The converted dose rate via aerial monitoring poorly matches the results of ground measurement in the mountain and forest areas because the FSM does not consider topographical effects. To improve the conversion accuracy, we developed new methods to analyze aerial monitoring data using the topographical source model (TSM) based on the analytical calculation of the -ray flux. The ARM results converted using both the FSM as well as TSM were compared with ground measurement data obtained after the FDNPS accident. By using TSM, the conversion accuracy was improved.