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NEXAFS analysis and electronic state of cesium in clay minerals

土壌中セシウムのNEXAFS分析と電子状態

鈴木 知史; 吉田 啓之; Shuh, D. K.*; 鈴木 伸一; 矢板 毅

Suzuki, Chikashi; Yoshida, Hiroyuki; Shuh, D. K.*; Suzuki, Shinichi; Yaita, Tsuyoshi

粘土鉱物中のセシウムの状態を評価するため、Csを含んだ粘土鉱物のCs M$$_{4,5}$$吸収端近傍X線微細構造(NEXFS)を測定するとともに、Csハロゲン化物や粘土鉱物を密度汎関数法(DFT)を用いて評価した。Csハロゲン化物の評価から、内殻空孔と価電子の相互作用を取り込むには、内殻空孔強度(CHS)を設定すればよいことが分かった。この結果に基づいて、粘土鉱物のCs M$$_{4,5}$$ NEXAFSをDFTより計算したところ、主ピークだけでなくテール構造を含めて実験結果をよく再現した。また、粘土鉱物の六員環のSiをAlに置換すると明確にNEXAFSは変化し、層間においてCsとKが共存する場合はNEXAFSの変化は小さかった。さらに、CsClと粘土鉱物中のCsの電子構造を評価した。

We evaluated Cs M$$_{4,5}$$ near edge X-ray absorption fine structure (NEXAFS) of Cs halides and clay minerals containing Cs using DFT calculation with the NEXAFS of the clay minerals measured. The evaluation of Cs halides indicated that the core-hole strength (CHS) in the NEXAFS measurement was reduced to 0.6, taking into account the strength interaction of the core-hole with the valence-band electrons. On the basis of this result, Cs M$$_{4,5}$$ NEXAFS of the clay mineral was well reproduced including the dominant peak and tail structures using DFT calculation. Moreover the calculation showed that the NEXAFS clearly changed with the displacement of Si atoms to Al in the six-membered ring of clay minerals and little did with the coexist of K atoms with Cs between layers of the clay mineral. In addition, we examined the electronic state of CsCl and the clay mineral containing Cs.

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