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Radioactive cesium (Cs) released by nuclear accidents is sorbed and fixed onto soil surfaces, which then radiate strong gamma rays (γ-rays). Decontamination around dwelling areas is now eagerly being implemented but more efforts are necessary to reduce the air radiation dose. Paddy field ponding, from the viewpoint of cost-effectiveness, is considered to be an effective practice for reducing the air radiation dose in the environment. In this study, field experiments were conducted at Sasu and Komiya regions in Iitate Village to verify the effectiveness of paddy field ponding, and numerical experiments were also conducted using the formula for uncollided γ-ray fluxes passing through the shield material. It was found that the a ponding water depth of 20-25 cm can drastically reduce the number of γ-ray photons emitted from the paddy fields, and the reduction in radiation dose was related to water depth. However, some differences were also observed between field and numerical experiments. The numerical calculation showed that the radiation dose decreased exponentially when the depth increased; however, field experiments showed a linear decrease. The cause might be the buildup effect caused by Compton scattering, but the details are unclear. It is necessary to explain these differences before ponding becomes a useful practice.
Kubo, N., Iida, T., & Mizoguchi, M. (2016). Reduction of air radiation dose by ponding paddy fields. In Agricultural Implications of the Fukushima Nuclear Accident: The First Three Years (pp. 189–204). Springer Japan. https://doi.org/10.1007/978-4-431-55828-6_15