HIGH-RESOLUTION NEUTRON-SCATTERING WITH COMMERCIAL THIN SILICON-WAFERS AS FOCUSING MONOCHROMATORS

Quasielastic scattering measurements with commercial silicon wafers as focusing monochromator and analyzer in a three-axis spectrometer show ed energy-transfer resolutions in the 10-100 mu eV range (fwhm). Resol utions were better and intensities higher than in a conventional arran gement with Seller collimators and pyrolytic graphite (PG) monochromat or and analyzer. Resolution remained high when extended-plate samples were used in focusing orientation. At cold sources, this technique wou ld give 10-20 mu eV resolutions at neutron energies near the peak of t he spectrum. Projections of resolution ellipsoids were determined by d iffraction from powder samples. The orientations of the ellipsoids are controlled by horizontal curvatures and can be rotated 90 degrees for high Q-resolution. A monochromator unit with remote control of horizo ntal curvature and fixed vertical curvature set to spatial focusing at the sample position was also tested. The strong vertical focusing gav e a significant gain in integrated intensities, but worsened the resol ution because of second-order aberrations. (C) 1998 Elsevier Science B .V. All rights reserved.