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.
How we decided what type of low-q instrument to build
At the ANSTO workshop "Pushing Small-Angle Neutron Scattering at OPAL to Smaller Q" held in November 2007 it was concluded that there is a strong scientific case with broad scientific application and a pre-existing low-Q user community in Australia. Two options for a new low-Q instrument to be built at OPAL were defined:
- Classical Crystal-USANS (or Bonse-Hart1 USANS)
This method uses perfect Si crystals in Bragg reflection as collimators.
- Spin-Echo SANS
This recently developed method uses spin precessions of a polarized neutron beam to encode the scattering angle to very high precision.
To help decide on the most appropriate type of instrument for the Australian community, we have carried out a detailed comparison of the capabilities of both methods. Based on experimental round-robin test measurements as well as analytical calculations, we analysed the strengths, weaknesses and experimental limitations, and investigated possible performance gains for both set-ups at OPAL.
- Round-Robin Neutron Scattering Measurements
Round-robin test measurements have been performed on a set of standard samples using the BT-5 USANS instrument at NIST and the SESANS instrument at Delft, respectively, to experimentally determine the advantages and disadvantages of both techniques. The standard samples consisted of polystyrene microspheres featuring different particle diameters and various scattering powers.
- Instrument Performance Estimations
Monte Carlo and analytical calculations helped estimate the performances of either instrument type, Crystal-USANS and SESANS, being installed at OPAL.
Although both techniques are applicable for studying large-scale objects they have different strengths, and it follows that different science will be done on these two instruments which are complementary rather than competitive. A survey of the Australian large-scale structures science community reveals that a rather large range of scientific problems will need to be covered by the new instrument. According to the experts, Crystal-USANS is better suited for investigating the widest possible range of sample properties and the widest range of sample scattering powers.
A paper titled "Crystal-USANS and SESANS: A Comparison of Two Neutron Scattering Techniques Applicable for the Study of Large-Scale Structures" will soon be published.
1Bonse, U. and Hart, M., Appl. Phys. Lett. 7 (1965) 238