OPTIMIZATION OF A DOUBLE BENT-CRYSTAL DIFFRACTOMETER FOR NEUTRON SMALL-ANGLE SCATTERING EXPERIMENTS

The optical properties of a double bent-crystal diffractometer utilize d in medium-resolution small-angle neutron-scattering experiments have been studied in detail. The expressions for the angular resolution of this device, represented by a statistical dispersion of its instrumen tal curve, were derived under the assumption of a simple beam collimat ion. In contrast to the conventional step-by-step measurements in Brag g reflection geometry, the use of fully asymmetric analyzer geometry w ith a position-sensitive detector, proposed previously, makes the tota lly nondispersive setting possible for any angular resolution set by t he monochromator bending. These conclusions are supported by Monte-Car lo simulations and experimental data.