A mosaic crystal backscattering monochromator for high-resolution powder diffraction

The resolution function of a powder diffractometer at a synchrotron radiation source increases with increasing Bragg angle of the monochromator. Consequently, a monochromator close to backscattering has been designed and built. Two mosaic crystals of beryllium in nondispersive setting serve as optical elements. They are mounted on goniometer heads inside a tube-like housing which may be evacuated. Fine adjustment of one of the crystals is done with a micro-goniometer driven by a magnetostrictive actuator. The fact that the housing is a tube allows the use of the assembly as part of a multi-purpose monochromator system for powder diffraction