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Bilby - Small Angle Neutron Scattering

Our first small-angle neutron scattering instrument Quokka has been so strongly oversubscribed (as at other neutron centres) that we have built a second instrument, Bilby. The principal difference between Bilby and Quokka is the ability of the former to operate in time-of-flight mode using a wide range of wavelengths (from 2 to 20Å) in a single measurement.

When the time-of-flight mode is not suitable, Bilby can utilise the Neutron Velocity Selector, operating as a conventional monochromatic pinhole SANS instrument.

In addition, 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 3.5% 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 (1-10nm), 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.

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 an option is to be likely to 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.

The construction of Bilby was funded as part of the Australian Governments Super-Science Initiative, its conceptual design was completed in early 2010, commissioning was finished in 2015. The instrument currently operating is located on the build-on-purpose CG2A cold neutron guide, OPAL's liquid-deuterium cold neutron source.

The instrument is named after the Australian mammal Bilby Macrotis lagotis.