The small-angle neutron scattering spectrometer at the National Bureau of Standards

A small-angle neutron scattering spectrometer, suitable for the study of structural and magnetic inhomogeneities in materials in the 10 to 1000 Å range, has been constructed at the National Bureau of Standards Research Reactor. The instrument is 8 m long and utilizes a mechanical velocity selector and pinhole collimation to provide a continuous incident beam whose wavelength is variable from 5 to 10 Å. The neutron detector is a 65 × 65 cm position-sensitive proportional counter which pivots about the sample position to extend the angular range of the spectrometer. Features unique to this instrument include a multibeam converging collimation system for high-resolution measurements and an interactive color graphics terminal with specialized software for the rapid imaging and analysis of data from the two-dimensional detector. The design and characteristics of the spectrometer and data acquisition system are described in detail and examples of data are presented which illustrate its performance.