The 40 m general purpose small-angle neutron scattering instrument at Oak Ridge National Laboratory

A series of upgrades have been undertaken at the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory, including the installation of a supercritical hydrogen moderator (T ≃ 20 K), which has boosted the flux of long-wavelength neutrons by over two orders of magnitude. In order to take advantage of the new capabilities, a 40 m-long small-angle neutron scattering (SANS) instrument has been constructed, which utilizes a mechanical velocity selector, pinhole collimation and a high-count-rate (>10⁵ Hz) large-area (1 m²) two-dimensional position-sensitive detector. The incident wavelength (λ), resolution (Δλ/λ), incident collimation and sample-to-detector distance are independently variable under computer control. The detector can be moved up to 45 cm off-axis to increase the overall Q range [<0.001 < Q = (4π/λ)sinθ < 1 Å^-1, where 2θ is the angle of scatter]. The design and characteristics of this instrument are described, along with examples of scattering data to illustrate the performance.