The plumes of Maralinga: Mapping nuclear fallout patterns over sixty years after atomic bomb testing

The British government conducted seven nuclear bomb tests and hundreds of other tests with radioactive materials at Maralinga in South Australia during the 1950s and 1960s. Little information was made available to the Australian public at the time of the blasts, and many details of the tests are still not publicly known. Several clean-ups of the nuclear test sites, two shortly after the end of testing by the British in 1964 and 1967, and one by the Australian government in 1994-1998 following a royal commission, focused on the areas closest to the blast sites where the radioactive contamination was greatest. In this study, we show that the distribution of radionuclides following the nuclear tests at Maralinga over 60 years ago can be extracted from publicly available conventional airborne gamma-ray spectrometry data acquired in 2018. We compare two methods to extract the 137Cs and 241Am signatures. An ENE-trending plume of 137Cs contamination is visible for at least 70 km despite the relatively low spatial resolution of the regional dataset. A clear signature for 241Am, a daughter product of the plutonium dispersed by the so-called 'minor' trials, was also extracted. Our results show that, despite the clean-ups at Maralinga, radioactive material remains over an area of approximately 3000 km2 and is readily detected by regional airborne surveys designed for mineral exploration.