The 30 m small-angle neutron scattering instruments at the National Institute of Standards and Technology

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 Angstrom(-1) in scattering wavevector, corresponding to structure in materials from 10 Angstrom to nearly 4000 Angstrom. The design and characteristics of the instruments, and their modes of operation, are described, and data are presented which demonstrate their performance.