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College Park, Maryland      June 6 - 10 , 2004

M2-C4 (11:30 AM): Performance of a Thermal-Neutron Double-Crystal Diffractometer for USANS at NIST

J. G. Barker, C. J. Glinka, J. Moyer, M-H. Kim (NIST Center for Neutron Research), A. R. Drews (Ford Motor Company, Dearborn, MI), M. Agamalian (Spallation Neutron Source, Oak Ridge National Laboratory)

An ultra-high-resolution, small-angle neutron-scattering (USANS) double crystal diffractometer (DCD) has been constructed at the NIST Center for Neutron Research (NCNR). The instrument uses multiple reflections from perfect single crystal silicon (220), before and after the sample, to produce a low instrument background suitable for small angle scattering measurements. The minimum detector background to beam intensity ratio is 5x10-7. The instrument is located on a dedicated thermal neutron beam port, utilizing 2.38 wavelength neutrons, producing a 17,000 cm-2s-1 peak neutron flux at the sample. The measurement range of the instrument extends from 3x10-4 nm-1 to 0.2 nm-1 in scattering wavevector (q), corresponding to structure size information in materials ranging from 30 nm to 20,000 nm. If the capability of the DCD is combined with the NCNR's 30 m long pinhole type instruments covering 0.01 nm-1 to 6.0 nm-1 in q, structure in materials from 1.0 nm to 20,000 nm can be measured. The design and characteristics of the instrument, and the mode of operation, are described, and data are presented which demonstrate the instrument performance.

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