Nuclear Reaction Analysis (NRA)
Principles: Unlike PIGE where gamma rays emitted in the nuclear reaction process are detected, in NRA the charged particles are detected. Not all nuclear reaction processes result in the emission of gamma rays. As in PIGE, this method is restricted to the determination of light elements.
However, as the emitted charged particle reaction products have to exit from the material, the NRA method is most sensitive to the region near the surface. By measuring the energy spectrum of the emitted charged particles, a concentration versus depth profile can be obtained for selected elements in the near surface region.
Applications: Nuclear Reaction Analysis (NRA) has mostly been applied to problems in materials science, where the use of isotopically enriched compounds allows the profile of a specific element to be targeted by ion beam reactions with its isotopes.
For example, in the thermal oxidation of silicon, the growth kinetics and diffusion of oxygen across the Si/SiO2 interface region has been studied using sequential oxidations in natural and 18O enriched oxygen gas. This isotopic specificity of NRA allows the differentiation between possible reaction pathways.
Example: The same technique as used in materials science has also been applied to help solve the nutritional requirements of endangered native fauna. Many Australian animals inhabiting thearid zone are faced with long periods of poor or inadequate nutrition during periods of low or no rainfall, and must depend for their survival on the efficient utilisation of their stored body reserves.
An understanding of their caloric usage is essential for determining their energy and protein requirements. These may then be correlated with the measured availability of natural resources, and help provide guidelines for wildlife managers in developing effective conservation strategies.
The specialised habitats that native animals live in are shrinking steadily, and an understanding of their habitat and requirements are essential for the survival of the species. Biological tracers using enriched stable isotopes are being used to monitor changes in free-ranging animals in the field.
The quantities of these isotopic tracers are being measured using ANSTO?s ion beam accelerators. This work underpins the research program being carried out at the Department of Zoology at the University of Western Australia.
Native animals are dosed with a small quantity of water enriched with the stable isotope 18O, and a blood sample is taken some hours later when isotopic equilibrium is reached. The animals are then left to roam freely for a few days in their natural environment, before a second blood sample is taken. The 18O content of the two blood samples is then measured using isotopic analysis on ANSTO's STAR Accelerator.
By measuring the loss of the stable isotopic tracer 18O from the animal as a result of isotopic exchange with the environment, the rate of production of carbon dioxide can be estimated, and thus the metabolic rate of the free-ranging animal. This information enables the quantification of the animal's energetic requirements.
A diverse range of small Australian animals such as the desert Dragon (Ctenophorus nuchalis) living in the Pilbara region of Western Australia, and the unique nectar and pollen-feeding Honey Possum (Tarsipes rostratus) in the south-west of Western Australia have been studied.