Optimization of highly oriented pyrolytic graphite applied to neutron crystal optics

The neutron diffraction properties of highly oriented pyrolytic graphite (HOPG) are reviewed using experimental results that have been obtained by diffraction of high-energy gamma rays, X-rays and neutrons. The interpretation of the empirical data based on diffraction theory leads to generic diagrams that display the performance of HOPG as a function of crystal thickness, mosaic spread and neutron wavelength. The analysis of the relation between the defect structure and diffraction properties demonstrates the usefulness of a detailed X-ray diffraction study to maximize the efficiency of composite neutron monochromators and analyzers. The optimization procedure is illustrated by the configuration of a double-focusing monochromator.