Statistical analysis on the air-dose rate in Fukushima Prefecture

We propose a stochastic model called as the Ornstein-Urlenbeck process in order to reproduce the fluctuations in the air-dose rate, measured in Fukushima. The significance of using the stochastic process is that the fluctuations in the dose rate, which includes various environmental changes specific to the observation site, may be considered, as well as the probabilistic behaviors of radioactive decay or of monitoring devices. We estimate the values of the model parameters and found that data of Iwaki and Kawamata follow the Ornstein-Uhlenbeck process correctly. The model enables us to detect abnormal dose rate, depicted in Fig. 9. (author)