b'FeatureAirborne radiometrics over Maralinga - call for a new survey 1990s. The Figure 16 image (processing and imaging by Pavel Jurza) is post clean up-revealing the reduction of plutonium close in to the test ground zeros (as indicated by the arrow).DiscussionPlutonium 239Weapons grade plutonium is created in a nuclear reactor by neutron bombardment of uranium 238. Plutonium 238, plutonium 239, plutonium 240, plutonium 241 and plutonium 244 are created in various combinations depending on the time spent in the reactor. The isotope plutonium 241 is usually about 2% of the mix. Its daughter, americium 241, has a strong gamma photopeak at 0.0595 MeV which serves to identify plutonium isotopes to a survey aircraft.Most forms of plutonium emit alpha particles, which are not Figure 14. Fugro 2005 survey. Cs-137 activity derived from Cs-137/K-40very harmful outside the body, but can be very damaging when ratio normalised from EG&G values. Ground zero sites indicated by circlesinhaled. When plutonium particles are inhaled, they lodge in the (processedby Joe Kita).lung tissue. The alpha particles can kill lung cells, which causes scarring of the lungs, leading to further lung disease and cancer. 10.2cmx10.2cmx40.33 cm. The volume of NaI(Tl) crystalPlutonium can enter the blood stream from the lungs and was 33.56 litres with a surface area of 1.482 m . The outputtravel to the kidneys, meaning that the blood and the kidneys 2of each sodium iodide crystal was computer controlled withwill be exposed to alpha particles. Once plutonium circulates automatic gain correction. Each block of four crystals had itsthrough the body, it concentrates in the bones, liver, and spleen, own Data Processing Unit. The equipment was mounted in aexposing these organs to alpha particles. Cessna210aircraft.SurveyingThe \x1cying height was 60 m and the line spacing was 200 m. The aircraft speed was approximately 70 m/s.ProcessingIn processing the Thompson Aviation 2018 survey the full spectrum processing method was employed involving the Praga-4 full spectrum processing extension of Geosoft Oasis Montaj software. The Cs-137 photopeak at 66.2 keV was extracted directly by full-spectrum \x1etting method, whilst a ratio of SignalFigure 15. Am-241 activity image, Thomson survey 2018 (GDA94/MGA53 Window and Background Window was used to extract theprojection).Am-241 response. The Signal Window around 59.5 keV was set to 6-80 keV whilst the Background Window was set to 100-180 keV. The weighted least-square \x1etting process uses a set of detector adjusted model responses to \x1end contributions of individual nuclides to the input spectrum. Corrections for scattering and attenuation by air column are included in the design of the detector model response. ResultsThe caesium 137 image is illustrated in Figure 2. Am-241 is imaged in Figure 15 whilst activity of Am241 was converted to those of Pu-239 by multiplying by an absorption factor of 1.33 and then by a ratio Pu 239/Am241 of 8.3. The new values thus obtained are illustrated in Figure 16. No account had been taken of the \x1enal clean up at Taranaki. This will clearly distort the calculations as the higher values will be absent in the cleaned- Figure 16. Pu-239 Thomson survey 2018 (GDA94/MGA53 projection). The up area. The values can only therefore be indicative. Taranaki ground zero Pu-239 activity is minimal which may indicate e\x1cects of the \x1dnal clean up (arrow). The striations northeast/southwest are the e\x1cects The americium contour map of Maralinga was compiled byof sand dunes intercepting the Pu239 particles (processing and imaging by EG&G in 1987 (Figure 9) before the major clean-up of the earlyPavelJurza).54 PREVIEWAPRIL 2024'