Novel multiple-beam very small angle neutron scattering (VSANS) using a conventional SANS instrument

Abstract

This article demonstrates how a small-angle neutron scattering (SANS) instrument, such as D33 at the Institut Laue–Langevin, can be configured without extensive modification to produce multiple highly collimated beams for measurements at the smallest scattering angles. This extends the range of material length scales able to be studied to greater than 1 µm, almost one order of magnitude greater than that of a conventional SANS instrument. The multiple-beam configuration uses the intrinsic properties of the neutron guide system and source and sample apertures with no additional optical devices or precise aperture array alignments. Up to several hundred individual beams, separated in angle by fractions of a degree in both the horizontal and vertical directions, can be extracted, which focus at the sample and diverge towards the distant neutron detector. This is particularly useful for the study of small samples, which can be probed at the smallest scattering angles while retaining sufficient neutron flux because of the use of multiple beams. The resulting data on the area neutron detector consist of multiple scattering or diffraction images which extend over and overlap those produced by neighboring beams. While the principle of the technique is rather simple, analysis of the overlapping SANS patterns requires the development of software techniques to extract the single scattering function.