Development of asymmetric reflection-type germanium monochromator for neutron beam enhancement

Yamauchi, Hiroki   ; Ishii, Yoshinobu*; Igawa, Naoki   ; Fukazawa, Hiroshi; Utsumi, Wataru

The neutron powder diffractometer, HRPD, can provide high-resolution data that meet the many users' needs until now. On the other hand, the demand of high-efficiency is growing in the recent years. In order to improve the source intensity and measurement efficiency, the authors tried to develop asymmetric reflection-type Ge monochromators. The mosaic crystals (20 in the horizontal direction) were cut at an angle of 40 relative to the Ge,3,3,1 reflecting planes. The diffraction results of standard Si samples reveal that peak intensities by the asymmetric type are improved 1.2 times larger than those by the existing symmetric type, but integrated intensities are almost comparable each other. For mosaic crystals, asymmetric reflections in compression geometry intensify the current density, but reflectivity is always less than that in symmetric reflections, and thus the suppression of the reflectivity just cancels out the enhancement of the current density.