Development of analysis method for airborne radiation monitoring using the inverse problem solutions

Sasaki, Miyuki  ; Ishizaki, Azusa  ; Sanada, Yukihisa   

Since the accident at Fukushima Daiichi Nuclear Power Station (FDNPS), some unmanned vehicles (UAVs) are applied to airborne radiation measurement in around FDNPS. In conventional analysis methods, count rate that is obtained in the sky is converted to air dose rate at 1 m above the ground (agl.) under following premises. (1) Topography under the UAV is a plane (plane source model). (2) The air dose rate at 1 m agl. under the UAV is constant inside approximately 10 m radius. (3) Relationship of altitude and count rate is exponential correlation. Therefore, it is difficult that dose rate by airborne radiation measurement is precisely measured at the mountains and uneven place of dose rate by the conventional method. In this study, Maximum Likelihood-Expectation Maximization (ML-EM) method which is used in the medical radiation such as Positron Emission Tomography (PET) is attempted to apply to environmental radiation measurement using UAV.