X線吸収微細構造(XAFS)が拓く地球・環境化学の新しい展開:炭酸塩に取り込まれた不純物の存在状態解析を例に

Abstract

X-ray absorption fine structure (XAFS) is a powerful element-specific probe which can be used to determine the local structure around a specific absorbing element and elemental speciation of absorbing element in any phases. XAFS in a fluorescence mode offers the advantage of element-discrimination and potentially high sensitivity to trace element. XAFS is therefore practically the only method for the structural characterization of trace elements in solid materials. XAFS has two different fine structures known as X-ray absorption near edge structure (XANES) and Extended X-ray absorption fine structure (EXAFS). XANES region extends from a few eV above the pre-edge to 50 eV above the edge. XANES gives the information on chemical species, valence, on site geometry and bond angles of absorbing atoms. On the other hand, EXAFS region extends from 50 eV to as much as 1,000 eV above the edge. EXAFS gives the information on the bond distance from the absorber and the number and type of backscatters. Applications of XAFS to geochemical and environmental science fields have been developed during the last decade. They will provide a tool for the elemental speciation of environment pollutants in various materials and the basic information for the discussion of geochemical processes. Examples included the present XAFS study of rare earth elements incorporated in synthetic calcium carbonate and others' XAFS studies of uranyl incorporated in natural and synthetic calcite. Finally, the feature of XAFS in the fields of geochemistry and environmental science was described.