ANSTO's research capabilities, led by the OPAL nuclear research reactor and associated instruments provide access to users investigating areas as diverse as materials, life sciences, climate change and mining/engineering.
Instrument Layout
USANS extends the Q-range of SANS to smaller Q values using a neutron beam with an extremely sharp angular profile which can be obtained by diffraction from a perfect crystal. The central parts of a USANS instrument are two channel-cut perfect Si single crystals (labelled monochromator and analyser) mounted on an optical bench. The monochromator crystal defines the beam that illuminates the sample, and imposes a strong correlation between scattering angles and wavelengths. Therefore, the USANS technique can use a relatively wide range of wavelength/scattering angle combinations simultaneously, which drastically enhances the flux on sample without sacrifying the Q-resolution.
During the experiment the measured scattering angle, or momentum transfer Q, is determined by rotation of the analyser crystal at which data are collected at one value of Q at a time. When a sample is inserted between these two components, small-angle scattering spreads the highly collimated beam, and this broadening is exhibited in the difference between the two rocking curves of the analyser, with and without sample.
As premonochromators we will use two bent vertically focusing, low-mosaic Si crystals, Si(111) and Si(311), in a sandwich setup, which will deliver two different wavelengths λSi(111) = 4.43 Å and λSi(311) = 2.32 Å to the instrument. With one sample position equipped with two interchangeable sets of channel-cut crystals, Si(111) and Si(311), allowing individual operation at different wavelengths we will be able to optimally accommodate weakly and strongly scattering samples.