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laboratory notes
The reflectivity and resolution properties of focusing cylindrically bent perfect crystal Si(111) monochromators of different diffraction geometries were tested with the aim of evaluating their possible use in a stress instrument with an unusually small take-off angle (2θM ≃ 30°). The experiments showed that an Si crystal with reflecting planes (111) in the symmetric diffraction geometry provides a maximum figure of merit for accuracy in the peak position that is comparable to that achieved previously from an optimized Si(220) monochromator at 2θM ≃ 55°.