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Polarization effects of X-ray monochromators modeled using dynamical scattering theory
Acta Crystallographica Section A: Foundations and Advances ( IF 1.9 ) Pub Date : 2021-05-27 , DOI: 10.1107/s2053273321003879 Marcus H Mendenhall 1 , David Black 1 , Donald Windover 1 , James P Cline 1
Acta Crystallographica Section A: Foundations and Advances ( IF 1.9 ) Pub Date : 2021-05-27 , DOI: 10.1107/s2053273321003879 Marcus H Mendenhall 1 , David Black 1 , Donald Windover 1 , James P Cline 1
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The difference in the diffracted intensity of the σ- and π-polarized components of an X-ray beam in powder diffraction has generally been treated according to equations based on dipole scattering, also known as kinematic X-ray scattering. Although this treatment is correct for powders and post-sample analyzers known to be of high mosaicity, it does not apply to systems configured with nearly perfect crystal incident-beam monochromators. Equations are presented for the polarization effect, based on dynamical diffraction theory applied to the monochromator crystal. The intensity of the π component relative to the σ component then becomes approximately proportional to |cos 2gθm| rather than to cos22gθm, where gθm is the Bragg diffraction angle of the monochromator crystal. This changes the predicted intensities of X-ray powder diffraction patterns produced on instruments with incident-beam monochromators, especially in the regions far from 2gθ = 90° in the powder pattern. Experimental data, based on well known standard reference materials, are presented, confirming that the dynamical polarization correction is required when a Ge 111 incident-beam monochromator is used. The dynamical correction is absent as an option in the Rietveld analysis codes with which the authors are familiar.
中文翻译：
使用动态散射理论建模的 X 射线单色器的偏振效应
粉末衍射中 X 射线束的 σ 和 π 偏振分量的衍射强度差异通常根据基于偶极散射（也称为运动学 X 射线散射）的方程进行处理。尽管这种处理对于已知具有高镶嵌度的粉末和样品后分析仪是正确的，但它不适用于配置有近乎完美的晶体入射光束单色器的系统。基于应用于单色器晶体的动态衍射理论，给出了偏振效应的方程。π 分量相对于 σ 分量的强度然后变得与 |cos 2gθ m |近似成正比。而不是 cos 2 2gθ m，其中 gθ m是单色器晶体的布拉格衍射角。这会改变在具有入射光束单色器的仪器上产生的 X 射线粉末衍射图的预测强度，尤其是在粉末图远离 2gθ = 90° 的区域。提供了基于众所周知的标准参考材料的实验数据，证实当使用 Ge 111 入射光束单色器时需要动态偏振校正。在作者熟悉的 Rietveld 分析代码中，动态校正没有作为一个选项。
更新日期：2021-07-01
中文翻译：
使用动态散射理论建模的 X 射线单色器的偏振效应
粉末衍射中 X 射线束的 σ 和 π 偏振分量的衍射强度差异通常根据基于偶极散射（也称为运动学 X 射线散射）的方程进行处理。尽管这种处理对于已知具有高镶嵌度的粉末和样品后分析仪是正确的，但它不适用于配置有近乎完美的晶体入射光束单色器的系统。基于应用于单色器晶体的动态衍射理论，给出了偏振效应的方程。π 分量相对于 σ 分量的强度然后变得与 |cos 2gθ m |近似成正比。而不是 cos 2 2gθ m，其中 gθ m是单色器晶体的布拉格衍射角。这会改变在具有入射光束单色器的仪器上产生的 X 射线粉末衍射图的预测强度，尤其是在粉末图远离 2gθ = 90° 的区域。提供了基于众所周知的标准参考材料的实验数据，证实当使用 Ge 111 入射光束单色器时需要动态偏振校正。在作者熟悉的 Rietveld 分析代码中，动态校正没有作为一个选项。
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