Charlwood, J.2025-07-162025-07-162022https://hdl.handle.net/2440/145987This item is only available electronically. Whole thesis (as available).Various nuclear fission and explosion trials were held at Maralinga, South Australia, by the United Kingdom from 1956 to 1963. Seven large trials each using atomic bombs of varying designs were detonated over this period. In addition to the seven large-scale trials, numerous minor trials were also performed within this period, and these are reported to have caused the greatest environmental impact to the area via dispersal of plutonium and uranium and related radionuclides. Fissile material used in the atomic weapons tested at Maralinga generally comprised 235U. Residual contamination is still present today in local soils. Although at greatly reduced levels it still poses a potential risk to humans through ingestion of airborne ‘hot’ particles which have a bulk composition of plutonium and uranium oxide. Enrichment of 235U in soils may therefore infer distribution of residual radionuclide contamination associated with historical atomic weapons testing. This research seeks to use the 235U/238U isotopic ratio obtained from Maralinga soil as well as control samples from various natural sources to generate a method that can constrain the limits of man-made nuclear contamination across Maralinga sites. Gamma spectroscopy was used to identify both natural and man-made radionuclides in samples. Analysis of bulk soils collected from across Maralinga test sites did not find a 235U enrichment within a 0.14% error margin (relative to the abundance of 238U) obtained through analytical uncertainty of uranium isotope measurements. The 235U/238U ratios of Maralinga soils and uncontaminated soils all presented a quasi-natural isotope ratio near the proposed value of natural uranium standard CRM 145 of 0.00725. However, gamma spectroscopy data shows that the Maralinga soils still contain an excess of various man-made radionuclides indicative of nuclear fission waste products such as 241Am, 137Cs and 152Eu. Neither induction-coupled plasma mass spectrometry or gamma spectroscopy analytical approaches used in this study were suitable for the detection of 239Pu. Overall, we conclude that 235U present from nuclear testing may be present at concentrations but do not significantly influence or vary from the ‘natural’ or background 235U/238U isotope composition. The uranium isotope ratio does not appear to be a beneficial marker of residual radionuclide distribution in the Maralinga area based on the limited number of samples assessed. Gamma spectroscopy assessment of collected soils infers radionuclide distribution is not homogeneous across the Maralinga area, Further assessment using a grid sampling approach would provide better resolution of radionuclide distribution across the Maralinga area.enHonoursGeologysoil contaminationenvironmental impactMaralinganuclear testingradionuclidesuranium isotopes‘Hot’ particlesThesis