Applying accelerator and microscopy methods for investigating radionuclides at Australia's former nuclear test sites

The radiological residues at the former British nuclear weapons testing sites in Australia at Maralinga, Emu and the Montebello Islands are of ongoing interest in terms of environmental fate, transport, and uptake of radioactive contamination into the biosphere. The physical and chemical characteristics of these residues govern their mobility in the various environmental zones in which they reside (surface soil, ocean sediment, active beach zones) and availability of the radiological components for uptake into living organisms. At the Taranaki site, Maralinga, substantial body burdens of Pu were observed in mammals and the pattern of organ uptake was found to match that reported for exposure to respirable radioactive particles bearing refractory Pu. In order to fully deconvolute the disposition and radio-ecological impact of the contamination at these sites it was necessary to study in detail the radioactive particle composition.
Plutonium often occurs in particulate forms at nuclear accident and test sites. Such particles require advanced techniques for characterisation including Accelerator Mass Spectrometry (AMS), Scanning electron microscopy and synchrotron X-ray fluorescence microscopy (XFM). Many such particles have core-shell structures where the surface is dominated by lighter elements sourced from local soils and the Pu concentrated in the interior. Particles formed during nuclear detonations and accidents can have complex structures and compositions which may be susceptible to variable leaching and weathering rates. Modelling results suggest that for respirable-sized Pu-bearing particles (that can be inhaled and lodged in the lung), most of the alpha emissions escape the particle and are deposited in the surrounding tissue. We are currently using advanced techniques to compare the radionuclide forms from the inland sites (Maralinga and Emu) with the marine site (Montebello Islands) to compare leaching and dose implications. The characteristics of the particles will largely determine the overall potential implications for long term fate of radiological contamination at the sites.