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A neutron spin filter based on transmission through nuclear-spin-polarized 3He gas has been applied to polarization analysis of small angle neutron scattering (SANS). Such spin filters, which are based on the large spin dependence of the absorption of neutrons by 3He, make SANS polarization analysis possible because of their large angular acceptance. In the present experiment, a 3He-based analyzer was employed to separate nuclear scattering into its coherent and spin-incoherent components. Polarized 3He analyzers were prepared by two different optical pumping methods and installed on the NG3 SANS instrument at the NIST Center for Neutron Research (NCNR). Measurements were taken on cellophane tape and silica gel, for which the scattering is almost completely incoherent and coherent, respectively, and on a combined sample. For the combined sample, separation of the coherent part from the incoherent part was successfully demonstrated using polarization analysis.

Two high-resolution, general-purpose, small-angle neutron scattering instruments have been constructed at the National Institute of Standards and Technology's Center for Neutron Research. The instruments are 30 m long and utilize mechanical velocity selectors, pinhole collimation and high-data-rate two-dimensional position-sensitive neutron detectors. The incident wavelength, wavelength resolution and effective length of the instruments are independently variable, under computer control, and provide considerable flexibility in optimizing beam intensity and resolution. The measurement range of the instruments extends from 0.0015 to 0.6 A−1 in scattering wavevector, corresponding to structure in materials from 10 A to nearly 4000 A. The design and characteristics of the instruments, and their modes of operation, are described, and data are presented which demonstrate their performance.

Approximate analytic expressions for determining the transmission of neutron benders which take into account reflectivity losses using the mean number of reflections agree well with computer simulation results which track the neutron trajectories directly, provided that the reflectivity is high. The exact calculation which can be performed using exponential integral functions for any value of the reflectivity is presented. Ray-tracing techniques for determining the transmission and number of reflections for non-perfect reflectivity can therefore be replaced by direct calculation.