Corrective refractive optics sharpens focus of SANS instrument. (General Developments).

Pioneering work done at the NIST Center for Neutron Research (NCNR), in collaboration with a private company, demonstrated that focusing a cold neutron beam with multiple biconcave lenses is a practical means of improving the resolution of long-flight-path, pinhole collimation, small-angle neutron scattering (SANS) instruments. Lens systems, consisting of linear arrays of up to 30 biconcave magnesium fluoride single crystals, are now used routinely on two 30 m SANS instruments at the NCNR nearly double of the size of microstructural features that can be resolved.

The lens system would be even more effective at longer wavelengths were it not for the spreading of the focal spot in the vertical direction due to gravity. A recent development has been to add large-apex-angle, single-crystal prisms in front of the lenses to correct for the gravitational aberration in the system. With the added prisms, the lenses are now effective at wavelengths up to 20 [Angstrom]. The combination of lenses and prisms now enables SANS measurements to be made at Q-values as low as 0.005 [nm.sup.-1], a full factor of 3 improvement over the previous conventional pinhole collimation. The new optics are enabling microstructural studies that link nanoscale with micrometer-scale features in, for example, polymer-clay nanocomposites, gels, and fluxoid lattices in superconductors.

CONTACT: Steve Kline, [phone]; [e-mail] or Boualem Hammouda, [phone]; [e-mail].