Time variation and strength distribution of air dose rate in Fukushima

The author investigated functions that describe the air dose rate data in Fukushima, as such functions provide the time dependence of decay in the environment and ratios of high dose rate areas. Data were published by the Fukushima Prefectural and Koriyama City governments. Time variation data were fitted with a superposition of exponential functions, whereas air dose rate relative frequency data were fitted with several functions (Gauss, gamma, q-Gauss, lognormal, and q-distribution). It was found that time variation data could be fitted well with a superposition of exponential functions and that the effective half-life of the radionuclide was markedly shorter than its physical half-life. Relative frequency data could be well fitted with a q-distribution. The strength distribution behaves like a power function for high air dose rate values (with an exponent <-4, where the exponent determines the behavior of the distribution for high air dose rate values). These findings are useful in estimating radiation exposure and high dose rate area ratios and are likely to be beneficial in protecting humans from radiation exposure.