A PERFECT MATCH FOR HIGH-RESOLUTION NEUTRON POWDER DIFFRACTION - POSITION-SENSITIVE DETECTION AND FOCUSING MONOCHROMATORS

Position sensitive detectors (PSDs) have been in use at MURR for nearl y 20 years, while focusing monochromators have been developed only dur ing the past six years. Incremental improvements in both systems have led to a high resolution powder diffraction system with a fast data ac quisition rate for small samples (typically one gram of material). Thi s is achieved by matching sample size to detector spatial resolution, by focusing in real space (two dimensional) and focusing in scattering with bent silicon monochromators. Fully open beams and large area det ectors make the performance of this method superior to the conventiona l one with Seller collimators and flat mosaic monochromators (vertical ly focusing). The use of inexpensive perfect Si crystals and linear po sition sensitive elements as well as the elimination of multiple Selle r slit assemblies also make this an extremely economical alternative. Improvements in electronics, data acquisition software and new, doubly focusing devices have opened the door to widespread use of high resol ution powder diffraction at small and medium flux facilities. (C) 1998 Elsevier Science B.V. All rights reserved.