Development of a High-Flux- and High-Temperature-Set-Up Bonse-Hart Ultra-Small-Angle X-ray Scattering (USAXS) Diffractometer

The conventional Bonse-Hart ultra-small-angle X-ray scattering (USAXS) diffractometer utilizes an asymmetric forecrystal in front of the symmetric grooved crystal in order to increase the flux collected from an X-ray source. To avoid the intensity loss resulting from mixing asymmetric and symmetric Bragg reflections, the forecrystal is carefully aligned with respect to the grooved crystal in such a way that the rocking curves from the asymmetric and symmetric Bragg reflections completely overlap. Our new monochromator for USAXS utilizes both asymmetric and symmetric Bragg reflections in the same rigid monolithic channel-cut 220 germanium crystal. It is therefore stable over a wide temperature range from 258 to 573 K without the use of a special constructing material with a very small thermal-expansion coefficient such as Super Invar.