5. Conclusions
The radioactive particles we collected from the polluted soil were larger and more active than Cs-bearing particles analysed by Adachi et al. (2013), Abe et al. (2014) and Yamaguchi et al. (2016), but their constituents were similar to, those of the reported aerosol particles. In addition, the present study demonstrated that silicates are one of the major components in the radioactive particle, and that the particle characteristics were different from those of so-called hot particles observed at the Chernobyl accident in 1986. We suggest that the present radioactive particles in the soil were discharged to the atmosphere during the same F1NPP emission event on 14 and 15 March 2011 with the source of previously reported Cs-bearing solid particles. Our results provide information on the temperature of materials ejected during the accident, some of which appear to have been molten. Our findings are useful to understand environmental dynamics studies of radioactive materials from the Fukushima accident. In addition, our findings have implications for the removal of the radioactive materials from the living areas and understanding of process of the accident. We suggest that additional investigations be conducted to analyse more particles from various distances from the F1NPP to elucidate the particle size–distance relationship, to determine the processes of synthesis of the particles in the reactor cores and peripherals, and to evaluate the effect of weathering on the particles in the environment.
