Application of X-ray absorption near-edge structure (XANES) using bent crystal analyzer to speciation of trace Os in iron meteorites
Application of X-ray absorption near-edge structure (XANES) using bent crystal analyzer to speciation of trace Os in iron meteorites
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DOI：
10.1016/j.aca.2005.11.043
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发表时间：
2006-02
影响因子：
6.2
通讯作者：
Y. Takahashi;T. Uruga;H. Tanida;Y. Terada;S. Nakai;H. Shimizu
中科院分区：
文献类型：
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作者：
Y. Takahashi;T. Uruga;H. Tanida;Y. Terada;S. Nakai;H. Shimizu
利用X射线吸收近边结构（XANES）谱研究了两颗铁陨石（Negrillos和班尼特县）中微量Os的形态，这两颗陨石的Os含量分别为65.7和58.3mg/kg，主量元素Fe+Ni含量均大于95 wt.%。在Os XANES测量过程中，强烈的Fe-K和Ni-K荧光和散射X射线作为背景噪声存在，比Os Lα荧光高4个数量级以上。为了排除不需要的X射线，使用了用于X射线荧光检测的布拉格几何形状的对数螺旋弯曲晶体分析仪，该分析仪与单元件纯Ge检测器和狭缝相结合。该系统使我们能够获得Os LIII边缘XANES光谱的两个铁陨石与更大的质量相比，记录在一个传统的荧光模式由19元素锗探测器没有分析晶体。此外，还测试了劳厄几何结构的市售晶体分析仪（BCLA，Oxford danfysik），其也给出了类似的高质量XANES光谱。布拉格几何结构比劳厄系统更有效地减少了由于背景X射线引起的噪声，而劳厄几何结构有效地收集目标荧光X射线，这表明使用劳厄分析仪与具有大的荧光检测接受面积的多元Ge检测器耦合可以获得统计学方面的更好的光谱。可靠的光谱形状的XANES测量，使我们能够模拟XANES光谱的Os在铁陨石中的一个高度定量的方式。采用对数螺旋晶体分析仪与锗探测器联用的系统是天然矿物和岩石中痕量元素形态分析的有力工具。
X-ray absorption near-edge structure (XANES) spectroscopy at the Os LIII-edge was measured for the speciation of trace Os in two iron meteorites, Negrillos and Bennett County, which contain 65.7 and 58.3mg/kg of Os, respectively, while major elements, Fe+Ni, are more than 95wt.%. During Os XANES measurement, intense Fe–K and Ni–K fluorescence and scattered X-rays existed as background noise, which were more than four orders higher than Os Lα fluorescence. To reject the unwanted X-rays, a log spiral bent crystal analyzer in Bragg geometry for X-ray fluorescence detection combined with a single-element pure Ge detector and slits was used. The system enabled us to obtain the Os LIII-edge XANES spectra of the two iron meteorites with greater quality compared with those recorded in a conventional fluorescence mode by a 19-element Ge detector without analyzer crystals. In addition, a commercially available crystal analyzer (BCLA, Oxford danfysik) in Laue geometry was also tested, and it also gave similar high-quality XANES spectra. The Bragg geometry reduced the noise due to background X-rays more effectively than the Laue system, while the Laue geometry was efficient to collect target fluorescence X-ray, suggesting that a better spectrum in terms of statistics could be obtained using a Laue analyzer coupled with a multi-element Ge detector with a large acceptance area for fluorescence detection. The reliable spectral shape of XANES measured enabled us to simulate XANES spectra of Os in iron meteorites in a highly quantitative manner. A system using log spiral crystal analyzer coupled with a Ge detector is a powerful tool for the speciation of trace elements in natural minerals and rocks.