原発南東方向で発見した既知のタイプに分類困難な放射性粒子

Uncategorized radioactive particles isolated from southwest region from the Fukushima Dai-ichi Nuclear Power Station

佐藤 志彦   ; 末木 啓介*; 石井 達也*; 五十嵐 淳哉*; Martin, P.*; Jones, C.*; Scott, T.*

Satou, Yukihiko; Sueki, Keisuke*; Ishii, Tatsuya*; Igarashi, Junya*; Martin, P.*; Jones, C.*; Scott, T.*

2011年に発生した福島第一原子力発電所(1F)事故では、放出したセシウムの一部がケイ酸化合物に取り込まれた不溶性Cs粒子として放出したことが判明している。このうち3月12日の1号機由来と15日早朝の2あるいは3号機からの放出が確認されているが、それ以外の事故イベントによる粒子の放出はまだ確認されていない。本研究では不溶性Cs粒子が報告されている1F北西地域以外で採取した土壌試料に探索対象を拡大することで、他の粒子放出のイベント有無、および新たな種類の放射性粒子の存在を調査した。

In Fukushima accident, insoluble radioactive Cs particles found at the northwestern region from the Fukushima Dai-ichi Nuclear Power Station (1FNPS). Presence of Cs particle in other surrounding area from 1FNPS is unclear yet. In the present study, the presence of other particle emission events and the presence of new types of radioactive particles were investigated by expanding the search object to soil samples collected outside the 1FNPS northwest region where insoluble Cs particles were reported. Four radioactive particles found from the samples. The particles look like pebbles and diameter is 0.4 to 2 mm, and the size feature is Type B. Isotopic ratio of Cs is very similar to type A of 1.0. EDS results confirmed the presence of iron and aluminum in addition to silicon. Further, in the CT image, there was an absorption point near the surface indicating that the element is heavier than iron. Although these features are clearly different from the insoluble Cs particles that have been reported in the past, in this implementation item it is not possible to find the location where Cs is adsorbed, and further direct emission from uranium or in the reactor.