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Observation of $$gamma$$-rays from fallout collected at Ibaraki, Japan, during the Fukushima nuclear accident

福島原子力事故時に茨城で採取された降下塵の$$gamma$$線スペクトルの観測

三枝 純; 菊田 恭章; 秋野 仁志

Saegusa, Jun; Kikuta, Yasuaki; Akino, Hitoshi

福島第一原子力発電所事故時(2011年3月)に茨城県で採取された降下塵の$$gamma$$線を測定した。塵は大型水盤内に捕集し、試料皿上に蒸発乾固した。その後、Ge検出器による測定を時期を変えて3度行い、各々の波高分布を精密に解析した。直後の測定では、50$$sim$$2048keVの範囲に約140本のピークが観測され、大部分はテルル,ヨウ素,セシウム同位体の全吸収ピーク及びサムピークであった。今回のデータを過去の原子力発電所事故時の浮遊塵のそれと比較すると、放射性セリウム,ルテニウム等の核種は検出されていない一方で、$$^{110m}$$Ag等多く検出されているものもあった。$$^{137}$$Csの放射能濃度は少なくとも1.4$$times$$10$$^{4}$$Bq m$$^{-2}$$であり、このうち14%が降雨によるものと推定された。

Measurements of $$gamma$$-ray pulse height distributions were performed for a fallout sample collected at Ibaraki, Japan during the Fukushima accident in March, 2011. The fallout was collected in a pan of water, then evaporated to dryness on a stainless-steel holder. The sample was measured by a germanium detector three times over a year. In the pulse height distribution of the initial measurement, approximately 140 peaks were observed between 50 and 2048 keV energy region. Most of them were either total absorption peak or the sum peak of Te, I or Cs isotopes. Compared to the fallout sampled at the past nuclear accidents, while some nuclides such as Ce and Ru were not detected, $$^{110m}$$Ag etc was prominently observed. Radioactivity concentration of $$^{137}$$Cs was estimated to be at least 1.4$$times$$10$$^{4}$$ Bq m$$^{-2}$$, approximately 14% of which was attributed to rainout.

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パーセンタイル:59.34

分野:Chemistry, Inorganic & Nuclear

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