title: First measurements of (236)U concentrations and (236)U/(239)Pu isotopic ratios in a Southern Hemisphere soil far from nuclear test or reactor sites.
abstract: The variation of the (236)U and (239)Pu concentrations as a function of depth has been studied in a soil profile at a site in the Southern Hemisphere well removed from nuclear weapon test sites. Total inventories of (236)U and (239)Pu as well as the (236)U/(239)Pu isotopic ratio were derived. For this investigation a soil core from an undisturbed forest area in the Herbert River catchment (17°30' - 19°S) which is located in north-eastern Queensland (Australia) was chosen. The chemical separation of U and Pu was carried out with a double column which has the advantage of the extraction of both elements from a relatively large soil sample (∼20 g) within a day. The samples were measured by Accelerator Mass Spectrometry using the 14UD pelletron accelerator at the Australian National University. The highest atom concentrations of both (236)U and (239)Pu were found at a depth of 2-3 cm. The (236)U/(239)Pu isotopic ratio in fallout at this site, as deduced from the ratio of the (236)U and (239)Pu inventories, is 0.085 ± 0.003 which is clearly lower than the Northern Hemisphere value of ∼0.2. The (236)U inventory of (8.4 ± 0.3) × 10(11) at/m(2) was more than an order of magnitude lower than values reported for the Northern Hemisphere. The (239)Pu activity concentrations are in excellent agreement with a previous study and the (239+240)Pu inventory was (13.85 ± 0.29) Bq/m(2). The weighted mean (240)Pu/(239)Pu isotopic ratio of 0.142 ± 0.005 is slightly lower than the value for global fallout, but our results are consistent with the average ratio of 0.173 ± 0.027 for the southern equatorial region (0-30°S).
authors.affiliation: Department of Nuclear Physics, Research School of Physics and Engineering, Australian National University, Canberra, ACT 0200, Australia. Electronic address: michaela.srncik@anu.edu.au.
authors.forename: M
authors.initials: M
authors.lastname: Srncik
authors.affiliation: Department of Nuclear Physics, Research School of Physics and Engineering, Australian National University, Canberra, ACT 0200, Australia.
authors.forename: S G
authors.initials: SG
authors.lastname: Tims
authors.affiliation: Department of Nuclear Physics, Research School of Physics and Engineering, Australian National University, Canberra, ACT 0200, Australia.
authors.forename: M
authors.initials: M
authors.lastname: De Cesare
authors.affiliation: Department of Nuclear Physics, Research School of Physics and Engineering, Australian National University, Canberra, ACT 0200, Australia.
authors.forename: L K
authors.initials: LK
authors.lastname: Fifield
mesh_terms: D001315:Australia; D065928:Forests; D013058:Mass Spectrometry; D009688:Nuclear Reactors; D010315:Particle Accelerators; D011005:Plutonium / Q000032:analysis*; D011834:Radiation Monitoring / Q000379:methods; D011847:Radioactive Fallout / Q000032:analysis*; D011868:Radioisotopes / Q000032:analysis*; D012987:Soil; D012990:Soil Pollutants, Radioactive / Q000032:analysis*; D014501:Uranium / Q000032:analysis*
chemical_list: D011847:Radioactive Fallout; D011868:Radioisotopes; D012987:Soil; D012990:Soil Pollutants, Radioactive; D014501:Uranium; D011005:Plutonium
keywords: (236)U; (236)U/(239)Pu; Accelerator Mass Spectrometry; Soil; Southern Hemisphere