2022 年 57 巻 3 号 p. 140-145
Relatively high levels of radioactivity were detected from the handball goal post that had been placed in the schoolyard of an elementary school in Nobeoka City, Miyazaki Prefecture, since around 1997. In November 2021, the goal post was to be removed, and it was transferred to a scrapping company through a waste disposer commissioned by Nobeoka City. Radiation monitoring at the time of transport detected the surface dose rates of 20–30 μSv/h at maximum from the pipe scale of the goal post. The goal post was found to have been apparently handmade by reusing scrap metal pipes. The components and radioactivity adhering to the interior of the pipe are measured and analyzed. Mineralogical analysis shows that the naturally occurring radioactive materials (NORM) contained mainly gypsum, gorgeyite, and baryte. The total radioactivity was evaluated to be 54.5 MBq to be equivalent to 226Ra by a preliminary estimation. The specific activity of the collected sample was 0.6 MBq/kg in the same nuclide. This case may be one of the typical examples of NORM in Japan, and four points in terms of radiation protection are discussed, clarification of the scientific and technical mechanisms of NORM generation, formulation of systematic and specific guidelines on the estimation of NORM according to the purpose of the evaluation, formulation of a comprehensive radiation protection strategy for NORM in Japan, and clarification of policies and procedures on sharing and disseminating relevant information to the public.
