OPTIMUM INTENSITY IN SMALL-ANGLE NEUTRON-SCATTERING - AN EXPERIMENTAL COMPARISON BETWEEN SYMMETRICAL AND ASYMMETRIC GEOMETRIES

Results of an experimental comparison of the performance of symmetric (with the flight path between source and sample, Ll, equal to the flight path between sample and detector, L2) and asymmetric (L1 not-equal L2) geometries of a small-angle neutron scattering instrument are reported. The comparison was performed under the assumption that a specific range of scattering vectors is required to be measured with a certain resolution. The measurements were performed at the spectrometer installed at the Riso National Laboratory, using as test samples a crystalline powder, a single crystal and a sample that produces a smooth scattering curve at small angles. The results obtained show that, when a specific scattering-vector range has to be measured with a specific resolution, the optimized asymmetric spectrometer performs better than the symmetric instrument. A simple graphical approach for the determination of the best geometry to perform a given measurement is introduced.