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Guidance for in situ gamma spectrometry intercomparison based on the information obtained through five intercomparisons during the Fukushima mapping project

Mikami, Satoshi, Ishikawa, Daisuke, Matsuda, Hideo, Hoshide, Yoshifumi, Okuda, Naotoshi, Sakamoto, Ryuichi, Saito, Kimiaki
Journal of environmental radioactivity 2019 pp. 105938
accidents, cesium, gamma spectrometry, nuclear power, power plants, radioactivity, radionuclides
Five intercomparisons of in situ gamma spectrometry by 6–7 participating teams were conducted between December 2011 and August 2015 at sites in Fukushima Prefecture that were affected by the fallout from the accident at the Fukushima Dai-ichi Nuclear Power Plant in March 2011. The evaluated deposition densities agreed within 5% and 4% in terms of the coefficient of variation for radiocesium (134Cs and 137Cs) and 40K, respectively, and the ratio of 134Cs/137Cs in deposition density agreed within 1% in terms of the coefficient of variation, by our best achievement through five intercomparisons. Two different methods for intercomparison were conducted: 1) simultaneous measurements in a narrow area within a 3 m radius; and 2) sequential measurements at an identical point. In a comparison between the two methods at a site where radiocesium was almost homogeneously distributed, no significant difference was observed between the results. The guidance for intercomparison method was proposed based on our experience, and are expected to be used effectively to ensure the reliability of in situ spectrometry.