Abstract

One of the serious fears for Japanese society is contamination of radioactive substances due to the huge earthquake and subsequent Fukushima No 1 nuclear power plant disaster This paper proposes a detection method to identify diffusion sources of radioactive small particles in the air based on publicly available data which are composed of air dose rate amount of rain wind speed and direction Air dose rate is observed on each public monitoring point The nearest weather observation station for each public monitoring point concerning air dose rate is also identified to analyze the relationship between air dose rate and weather conditions This method focuses on all cases of continuous rainfall duration because various sizes of spike concerning air dose rate on a public monitoring point are observed among the cases Each spike starts when rainfall begins and the spike disappears when rainfall continues This is because rainfall cleans up radioactive particles in the atmosphere The method confirms a statistically significant difference of increase rate of air dose rate between each pair among rainfall cases It also identifies an existence range of direction of diffusion sources based on significance tests of correlation coefficients