Radioactivity of various kinds of natural samples and radiation dose rate were measured after the Fukushima Daiichi Nuclear Plant accident for finding the contamination of radioactivity.
Just after the nuclear accident, short life nuclides with half life of several days were observed in samples such as the soils of several places in Japan, plants and filtrated air samples. The decrease of dose rate corresponded to the decay of these nuclides. It was found that radioactive nuclides were strongly adsorbed by fallen leaves and weathered leaves compared with living plant surface.
Systematical survey was carried out at Aobayama area of Miyagi University of Education in 2011 and 2014. It became clear that radioactivity and dose rate were varied from place to place due to natural environment and phenomena or perturbation of people's activity. It was found that radiocesium stayed at the surface of soil, and not penetrated as the water soluble species，during these periods. As for surface soil samples, however, the results of the survey in 2014 made it plain that diffusion, transfer and accumulation of radiocesium have occurred. Radioactivity concentrations were less than physical one calculated from the result of 2011 and decay until 2014.
Similar survey was carried out at Sukagawa city in Fukushima prefecture.
東日本大震災後の環境中での放射能・放射線の推移
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東日本大震災後の環境中での放射能・放射線の推移
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