“To do really interesting science, you will have to use both neutrons and x-rays.”
This, says Michael James from ANSTO’S Bragg Institute, is the fourth law of neutron scattering.*
Mike’s objective at the Australian Synchrotron User Meeting in December 2011 was to encourage his audience to consider using both neutron scattering and synchrotron x-rays as probes of atomic and molecular structure. He described the main differences between the two techniques, presenting them as complementary, and followed up with an impressive set of research examples in which the techniques were used in combination to study the structure and function of a diverse range of advanced materials.
In brief, x-rays offer high flux; high resolution, excellent signal-to-noise and tuneable energies. However, they are surface-sensitive, and the scattering is dominated by large atoms (high Z). Neutrons, on the other hand, are highly penetrating, sensitive to light elements and spin-polarised (a valuable characteristic for investigating magnetism). Disadvantages of using neutrons include the relatively low flux and modest resolution.
Like x-rays, neutrons have the right wavelength to probe atomic and nanoscale structures. Neutrons interact with nuclei and not electron clouds, and can therefore distinguish between hydrogen and deuterium. They can also ‘see’ light atoms next to heavy ones, penetrate deeply into matter (non-destructively), and interact with magnetic materials. Neutrons are also a highly effective spectroscopic probe for studying the molecular vibrations and the dynamics of materials.
“Together, the Australian Synchrotron and the OPAL research reactor represent Australia’s largest-ever investment in scientific infrastructure,” Mike told his audience. “In isolation, each facility has hit its stride; with first generation beamlines completed and vibrant international user programs in place. Collectively, the use of neutrons and synchrotron light has aided the untangling of complex molecular and nanoscale problems with a deeper capacity than either probe alone.”
Seven of the first 13 neutron-scattering instruments at the OPAL research reactor are available for routine scientific operation, with the remaining six under various stages of construction. OPAL has two proposal rounds per year, and the next deadline is 15 March 2012.
* The laws of neutron scattering, according to Michael James (and first articulated by Prof. John White from ANU):
- All scattering patterns look the same (more or less)
- NEVER use neutrons unless you have to
- Eventually you will have to use neutrons
- To do really interesting science, you will have to use both neutrons and x-rays.
Photo above: Mike James from ANSTO describes the advantages of neutron scattering.