<title>Curved-crystal three-axis neutron spectrometry with position-sensitive detection</title>

Abstract

The neutron optics of three-axis spectrometers with bent perfect crystals and position sensitive detection (PSD) has been developed. Theoretical analysis in the phase space and in the scattering space shows that simultaneous PSD scans can be performed along any given direction in the scattering (h(omega) ,Q) plane, including energy transfer scans or Q- scans. For instance, to perform a simultaneous energy transfer scan the curvature of the monochromator must be set for 'monochromatic focusing' while the curvature of the analyzer must be significantly away from the 'monochromator focusing' value. A new kind of focusing was found to be possible. Under the right conditions the resolution in scattering becomes insensitive to the thickness of the analyzer crystal. Packets of commercial thin silicon wafers can then give resolutions corresponding to a single wafer at considerable gains in intensity. Control experiments with a 14-wafer assembly have confirmed this conclusion. Resolutions below 3 minutes of arc on the angular scale were obtained (corresponding to energy transfer resolutions in the range of 10 to 150 (mu) eV, depending on the neutron energy). A practical difficulty is that very high spatial resolutions of the PSD, in the submillimeter range, are needed to take full advantage of the possibilities offered by commercial thin silicon wafers.