200-mm segmented cylindrical figured crystal for von Hamos x-ray spectrometer

Abstract

A von Hamos Bragg crystal spectrometer at 1C beamline of Pohang Accelerator Laboratory for x-ray emission spectroscopy (XES) is described. Diced Si crystals of different orientations ([111], [110], [100], and [311]) are glued onto a planoconcave glass substrate having 250/500 mm radius of curvature. To enhance the spectrometer efficiency, the length of the crystal analyzer is kept 200 mm. The emission spectra of Cu foil and Fe foil and elastic scattering from Al foil are measured using the von Hamos geometry in which curved crystals disperse the x-rays. Spectrometer efficiency and energy resolution are measured at various x-ray photon energies. X-rays are incident at 6.54 keV, 9.00 keV, 9.205 keV, and 11.51 keV for Si(440), Si(444), Si(800), and Si(933) crystal analyzers, respectively. The cylindrical figured analyzer is placed near 80° with respect to the sample, which gives better energy resolution. The spectrometer efficiency of the Si(444) crystal analyzer increases by ∼2 times when the length of the analyzer is increased from 100 mm to 200 mm. Furthermore, to measure Fe Kα1, Kα2, and Kβ simultaneously, we made a mixed crystal analyzer in which alternative strips of Si[111] and Si[110] are glued onto one preshaped cylindrical substrate. The enhanced efficiency and simultaneous measurement of Kα and Kβ emission lines will give an edge over in situ and time-resolved x-ray emission spectroscopy studies. The information extracted with a high efficiency spectrometer from low intensity XES emission lines will be useful for the in situ elemental characterization in catalytic reactions.