Mosaic crystal X-ray spectrometer to resolve inelastic background from anomalous scattering experiments

We describe a mosaic crystal X-ray energy analyzing spectrometer to separate the inelastic scattering enhanced by radiation near an absorption edge from the elastic diffraction of interest for atomic site determinations. An important consideration is to minimize the sensitivity to changing source profile so that diffracted intensities are comparable over large angular ranges. Energy resolution limited mainly by fractional-mm source sizes is comparable to that with nearly perfect crystals. High spectrometer efficiency for the diffusely distributed X-ray scattering associated with amorphous materials and the weak Laue scattering from chemical order in crystalline solid solutions is achieved with a combination of sagittal and parafocusing from a mosaic graphite monochromator. Because of the mosaic nature of the crystal, the parafocusing geometry achieves meridional focusing for a magnification of 1:1, and a broad energy range proportional to the mosaic spread is dispersed along a linear position-sensitive detector for simultaneous detection. Energy resolutuion ΔE/E of 1/500 and lower is achieved in the 6-10 keV energy range tested. Though the sagittal radius is fixed, the spectrometer will operate effectively over an X-ray energy range of E±0.5 E with fixed focal distances. This mosaic crystal spectrometer offers similar advantages for X-ray spectroscopy experiments. (orig.)