Publikationsrepositorium - Helmholtz-Zentrum Dresden-Rossendorf

The radiological residues at the former weapons testing sites at Maralinga, Emu and the Monte Bello Islands often occur in particulate form (so called hot particles). Large numbers of these particles were emitted from nuclear and non-nuclear tests. For example each square meter in a plume which extends for tens of kilometres at the Taranaki site (Maralinga) can contain more than 3000 readily identifiable particles. The physical and chemical characteristics of these particles affect their mobility and availability for uptake into living organisms. When they contain long-lived radionuclides (e.g. 239Pu) these particles may slowly weather, and thus provide a persistent source of ionic forms, or smaller particles, for many thousands of years.
From these Australian sites, we have gathered a series of particles that have weathered and interacted with the environment for 50+ years since their initial formation and release events. The particles are being evaluated using a range of methods including gamma spectrometry, autoradiography, high sensitivity Accelerator Mass Spectrometry analysis (AMS), leaching studies, and synchrotron X-ray fluorescence microscopy.
Significant findings include the clustering of Cs on the exterior of a glassy fission fragment, with Sr occurring in the nearby interior, suggesting the 137Cs may be more available for weathering processes, and the beta emissions from the 90Sr may be largely self-shielded within the particle. In contrast, a different particle from a nearby site lacked any fission products, but contained Pu(IV) oxyhydroxides consistent with weathering in a semi-arid environment. Although the 239Pu is very active, detailed dose modelling suggests most of the alpha emissions from particles > 5µm are shelf-shielded within the particles themselves, and therefore impart lower dose than the equivalent Pu dissolved and distributed throughout an organ. However, when Pu exists on exterior surfaces, a hot particle that has been internalised (e.g. lodged in a mammalian lung) may produce relatively highly concentrated dose rates to adjacent tissues.