b'FeatureAirborne radiometrics over Maralinga - call for a new survey The history of airborne radiometric surveys over the nuclear test range at Maralinga and a call for a new surveyPat CunneenE pat@cunneen.bizIntroductionattempted to measure ground deposition associated with the detonations, but the plume did not coincide with the On 17 March 1992, as Managing Director of World Geosciencesampling array. The monitoring results obtained after the event Corporation, I instructed our airborne geophysics team in Southcontained systematic errors greater than a factor of ten as a Australia to over\x1cy the Maralinga atomic test range. Maralinga isresult of the methods used. A comparison between the levels north of Ooldea on the Trans Australia Railway Line. I instructedreported by the UK at the time and the \x1eeld results reported the crew to \x1cy low and slow and to set the spectrometer toby Australian Radiation Laboratory (Lokan 1985) demonstrated best observe any gamma rays which might be emitted from thean underestimate of the plutonium contamination by about an 36-year-old ground zero sites. order of magnitude (MARTAC 2003).The \x1erst \x1cight was a great surprise; the radiation, measured inAfter many ine\x1fective clean-up attempts and a Royal counts per second, was through the roof to the extent that theCommission (Royal Commission into British Nuclear Tests crew became slightly worried about their exposure levels. in Australia 1985), the Australian Government appointed After reviewing our own data, and all the airborne radiometrica Technical Advisory Group (TAG) to recommend \x1enal surveys since the end of testing 70 years ago, it is apparent thatrehabilitation procedures. The TAG recommended, among after all this time Maralinga has not yet been properly surveyed.other things, an airborne radiometric survey, an airborne A low-level close line spaced modern survey would be of greatmagnetic survey and a ground geophysical survey (Australian assistance to the management of the range. The raw WGC dataAtomic Energy Commission 1985). They highlighted have been lost in company takeovers and exist today only asplutonium contamination as a major concern. The two latter slides salvaged by Greg Street, and the o\x1bcial contour mapsrecommendations were ignored, apart from some sporadic of radioisotopes are copied from reports. Re-processing of theground spectrometer surveys along roads and fence lines. regional 2018 Gawler Craton survey data by Pavel Jurza, andHowever, the US Department of Energy was commissioned, of the 2005 SADME survey by Joe Kita, serves to illustrate howin 1987, to conduct an airborne radiological survey. It sub-much better a new survey would be. contracted EG&G Energy Measurements Inc, the manager of its nuclear test facility in Nevada, to \x1cy the survey. Background Details of surveysFrom 1952 until 1963 the British Government exploded twelve plutonium implosion type atom bombs in Australia, seven atApart from the survey by EG&G, four other radiometric surveys Maralinga in South Australia (Table 5). The devices were of thewere undertaken over Maralinga, between 1992 and 2018, for type exploded for the \x1erst time in the Trinity test in Los Alamosdiverse purposes (Table 1). in New Mexico in June 1945, and a few months later at Nagasaki in Japan. It was on 27 September 1956 that the British explodedFallout and detection of soil activation isotopes the \x1erst of the seven nuclear \x1ession devices. The last took place on 9 October 1957. The half-lives of isotopes directly or indirectly observed by the Several hundred Minor Trials involving \x1essionable material were\x1eve surveys at Maralinga are listed in Table 2.also carried out at Maralinga. The Minor Trials used explosivesThe half-lives of isotopes observed by EG&G were used to to blow up nuclear warheads containing plutonium, to simulatecalculate values at the time of subsequent surveys. The what would happen in an air crash. Also, twelve tests werespeci\x1ecations of the AGSO survey were such that only conducted at the Taranaki site in 1960, 1961 and 1963, resultingcaesium 137 was detected. WGC and AGSO could not detect in it becoming the most contaminated site at Maralinga. Theamericium-241 because the lower level of the total count tests were conducted on steel structures known as featherwindow was set too high at 300 keV, which was normal for beds. The tests produced jets of molten, burning plutoniumgeological surveys of naturally occurring elements.extending hundreds of feet into the air. The damage to the feather beds and their concrete stands was much greater thanMaximum activity concentrations of isotopes present at anticipated, and a new feather bed was used for each round. Atthe time of the surveys were calculated by multiplying the the conclusion of each test, all the debris was buried in nearbymaximums observed by EG&G by an absorption factor of 1.33 pits. Eventually there were 21 pits containing 830 t of material.(to correct for gamma rays absorbed by the soil cover) and then Uranium and beryllium were similarly exploded. applying the half-life of the particular isotope (Table 3). Cs-137 and Co-60 concentrations declined in accordance with their Gamma ray spectrometers mounted in aircraft were notrespective half-lives but Am-241, with a half-life of 432 years, available to the British in 1967, when they \x1erst attemptedincreased over time because its parent plutonium 241 has a to clean up the Maralinga site. It was reported that theyshorter half-life of only 14 years (Burns et al. 1995).APRIL 2024PREVIEW 47'