USING WAFER STACKS AS NEUTRON MONOCHROMATORS

A process to introduce a spatially homogeneous but anisotropic mosaic structure into thin, single-crystal wafers, which are then stacked and used as neutron monochromators, is described. The advantages compared to conventional techniques are good reproduceability, low cost and reduced risk of process failure. A focusing Ge(115) monochromator made from 24 wafer stacks was built for the high-resolution neutron powder diffractometer at the High Flux Beam Reactor at Brookhaven National Laboratory. Besides building ''classical'' monochromators for elastic neutron scattering experiments, individual wafers with a given peak reflectivity can be tilted with respect to each other to increase the reflected wavelength band Delta lambda/lambda. Such ''fanned'' arrays present a competitive alternative to monochromators using highly-oriented pyrolitic graphite (HOPG).