Combined USANS/SANS studies and current status of the multi-wavelength USANS instrument at SNS

Orateur : Dr. Michael AGAMALIAN (Oak Ridge National Laboratory - Spallation Neutron Source - USA)

Over the past fifteen years ultra-small-angle scattering (USANS) has emerged as a powerful new technique, which extends the dynamic range of supra-molecular structural investigations two orders of magnitude beyond what has been customarily accessible. Nowadays the experimentally measurable range of neutron molecular scattering corresponds to the range of internal diffraction distances in condensed matter from 10 Å to 10 μm. Thus the multilevel supra-molecular structure of liquids and solids containing not only nano-metrical particles but also aggregates and agglomerates can be described by analyzing neutron diffraction data. It is obvious that such a broad, extended over four orders of magnitude dynamic Q-range cannot be covered by one instrument ; the conventional 30m pin-hole SANS machine must be coupled with a USANS diffractometer. The upper limit of this range in real space corresponds to the smallest value of scattering vector or angle in reciprocal space ; therefore, ultra-high angular resolution is required to extend the conventional SANS range in the direction of larger diffraction distances. The currently best approach for achieving the highest resolution in reciprocal space is related to application of the Bonse-Hart Double-Crystal Diffractometers (DCD) for combined USANS/SANS measurements ; several classical examples demonstrate advantages of the USANS/SANS technique.

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