BILBY - 2nd Small-Angle Neutron Scattering Instrument
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More information on BILBY
Our first small-angle neutron scattering instrument QUOKKA has been so strongly oversubscribed (as at other neutron centres) that we have now built a second one, BILBY. The principal difference between BILBY and QUOKKA is ability of the former to operate in time-of-flight mode using a wide range of wavelengths (from 2 to 20 Angstroms) in a single measurement. In addition, to cover the same Q-range as QUOKKA, BILBY has two sets of detectors installed on two carriages which can move independently within the 18m-long vacuum vessel.
BILBY has two distinctive features. First is the possibility to control wavelength resolution within range between 4% and 30%. The second is the very wide dynamic Q-range (in order of thousand) accessible within a single measurement. If one pulses the neutron beam using four mechanical choppers, and measures scattering of neutrons of various wavelengths as a function of their time of flight from chopper system to detector, one can record a complete data set in a single instrument setting.
BILBY is very well suited for the study of kinetic effects, like relaxation following a chemical reaction, or external impulses like mechanical deformation, an electric or magnetic field.
Small-angle scattering is a powerful technique for looking at sizes and structures of objects on the nanoscale (1-100 nm), like polymer molecules, biological molecules, defect structures in metals and ceramics, pores in rocks, magnetic clusters, magnetic flux lines in type-II superconductors and so on.
ANSTO has both X-ray and neutron small-angle scattering adjacent to each other, and the advantage of neutrons is primarily for soft matter where the contrast-variation method can be used. In addition, it is useful for magnetic problems and ones in which large samples must be used.
In many ways, small-angle scattering is complementary to electron microscopy. While direct imaging is the domain of electron microscopy, SAXS and SANS can provide particle sizes, shapes and distributions averaged over a complete macroscopic sample.
Small-angle scattering is rarely able to solve a problem on its own, and is typically used in conjunction with a number of other techniques. SANS was crucial in showing that polymer molecules are self-avoiding random walks (Flory's prediction Nobel Prize in Chemistry, 1974), and that Type-II superconductors allow magnetic flux to penetrate, forming a lattice of magnetic vortices (Abrikosov's prediction Nobel Prize in Physics, 2003). Other major achievements have been understanding viscosity modifiers in lubricants, solving the coarse structure of the ribosome, understanding the nature and role of particulate additives to tyres, and the porosity of sedimentary rocks in oil and gas reservoirs.
Conventional small-angle scattering operates by defining a very well collimated beam using a pair of small well-separated circular apertures, and a roughly similar distance after the sample to a high-resolution detector. To go to smaller angles, there is a potential to use narrow slits instead of pin-hole collimation. Such option is to be likely be featured on BILBY.
The main features of BILBY are conceptually the same to the new D33 machine at the Institut Laue Langevin in Grenoble, France. Use of precise narrow slits will make it somewhat similar to the new VSANS instrument at NIST .
The construction of BILBY was funded as part of the Australian Governments Super-Science Initiative, its conceptual design was completed in early 2010, and it is located on the new CG2A cold neutron guide, viewing OPAL's liquid-deuterium cold neutron source.