A compact optical design for Bragg reflections near backscattering

A very compact in-line X-ray optical design is presented which is optimized for use with Bragg reflections close to backscattering (Bragg angles near 90 degrees). The essential idea is to use a low-order Bragg reflection to couple the X-ray beam into a small channel-cut backscattering crystal. The design is demonstrated in an almost theoretically performing high-resolution monochromator providing 2 x 10(8) photons s(-1) in a 0.52 meV bandwidth at 25.65 keV. The monochromator is used to measure inelastic nuclear scattering from phonons in Dy-161-containing samples.