Recent studies of highly oriented pyrolytic graphite and hybrid graphite-silicon monochromator systems

The excellent performance of highly oriented pyrolytic graphite (HOPG) as monochromator, analyzer and filter material for neutron instrumentation was discovered more than 50 years ago. Even though HOPG has been in use for a long time, there is still room for improvements regarding its optimized use in neutron beam conditioning. The features of a novel concept called POSI based on careful x-ray characterization of the HOPG crystals and on proven mounting and focusing technologies show that the efficiency of HOPG monochromators can be increased while decreasing complexity and cost. Moreover, by combining HOPG and bent perfect silicon crystals the functionality of separate single monochromators and analyzers can be expanded to a wider range of applications provided by dual systems or bichromators.