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Research Interests: Environmental Science, Chemistry, Uranium, Erosion, Sediment, and 3 moreIsotope, Soil Water, and PLUTONIUM
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Concentrations of 127I and 129I in rainwater samples from several stations across Argentina (latitudes between 25° S and 55° S) were measured and analyzed for the assessment of distribution patterns and potential sources of 129I in the... more
Concentrations of 127I and 129I in rainwater samples from several stations across Argentina (latitudes between 25° S and 55° S) were measured and analyzed for the assessment of distribution patterns and potential sources of 129I in the Southern Hemisphere. Measured 129I levels, clearly above those explainable by natural background and atmospheric nuclear weapons tests, can be understood by the injection into the Southern Hemisphere of 129I that had been discharged from nuclear fuel reprocessing plants in the Northern Hemisphere.
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Primary and secondary datasets associated used in this study
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ABSTRACT The isotopes (236)U and (239)Pu, both produced during nuclear weapons tests carried out in the 1950s and 1960s, are present in the environment and may be used as tracers for soil erosion studies. Although these radionuclides... more
ABSTRACT The isotopes (236)U and (239)Pu, both produced during nuclear weapons tests carried out in the 1950s and 1960s, are present in the environment and may be used as tracers for soil erosion studies. Although these radionuclides occur only at ultra-trace levels in nature, they can be readily measured by accelerator mass spectrometry with the 14UD heavy ion accelerator at the Australian National University. We have analysed a series of vegetation samples for their (236)U and (239)Pu concentration and compared the results with those found in the surrounding soil. (236)U could be measured in all collected samples whereas (239)Pu could not be detected in several vegetation samples due to its very low concentration, although it was readily detectable in the soil. We find that, relative to plutonium, (236)U is preferentially taken up by plants with enrichment factors ((236)U/(239)Pu)veg/((236)U/(239)Pu)soil that range between 7 and 52 in the present study. Copyright © 2015 Elsevier Ltd. All rights reserved.
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The nucleogenic isotopes 36Cl, 236U and 239Pu are produced naturally in subsurface environments via neutron capture of thermal and epithermal neutrons. Concentrations are, however, very low and accelerator mass spectrometry (AMS) is... more
The nucleogenic isotopes 36Cl, 236U and 239Pu are produced naturally in subsurface environments via neutron capture of thermal and epithermal neutrons. Concentrations are, however, very low and accelerator mass spectrometry (AMS) is required for quantitative measurements. A particular challenge is presented by the measurement of 236U/238U ratios down to the level of 10−13 that is expected from rocks with low
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Atmospheric testing of nuclear weapons during the period 1945–1980 ushered in the ‘atomic age’ and released large quantities of anthropogenic radiogenic nuclides into the atmosphere. These radionuclides were subsequently deposited as... more
Atmospheric testing of nuclear weapons during the period 1945–1980 ushered in the ‘atomic age’ and released large quantities of anthropogenic radiogenic nuclides into the atmosphere. These radionuclides were subsequently deposited as fallout to the entire surface of the planet. While many have decayed to negligible levels, long-lived radionuclides persist and will do so for thousands of years. Isotopes of plutonium, 239Pu (half-life 24 100 years) and 240Pu (half-life 6563 years), provide the best chronological markers for the onset of this anthropogenic event both now and into the future due to their long half-lives, particle-reactivity, and the fact that they were present in negligible quantities prior to anthropogenic production and release. Chronostratigraphic markers established by distinct Pu concentration profiles and Pu isotope changes in sediment sequences and ice and coral cores can provide high-resolution dating over the last 60 years. However, even though fallout has ceas...
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National Key Research and Development Program (2016YFA0600502) National Natural Science Foundation of China (41671466, 41773004).
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Unusually high concentrations of americium and plutonium have been observed in a sediment core collected from the eastern Lombok Basin between Sumba and Sumbawa Islands in the Indonesian Archipelago. Gamma spectrometry and accelerator... more
Unusually high concentrations of americium and plutonium have been observed in a sediment core collected from the eastern Lombok Basin between Sumba and Sumbawa Islands in the Indonesian Archipelago. Gamma spectrometry and accelerator mass spectrometry data together with radiometric dating of the core provide a high-resolution record of ongoing deposition of anthropogenic radionuclides. A plutonium signature characteristic of the Pacific Proving Grounds (PPG) dominates in the first two decades after the start of the high yield atmospheric tests in 1950's. Approximately 40?70% of plutonium at this site in the post 1970 period originates from the PPG. This sediment record of transuranic isotopes deposition over the last 55 years provides evidence for the continuous long-distance transport of particle-reactive radionuclides from the Pacific Ocean towards the Indian Ocean.
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RAYS USING COSMOGENIC NOBLE GASES AND RADIONUCLIDES ON IRON METEORITES. T. Smith1, I. Leya1, S. Merchel2, G. Rugel2, S. Pavetich2, A. Wallner3, K. Fifield3, S. Tims3 and G. Korschinek4. 1University of Bern, Space Research and Planetary... more
RAYS USING COSMOGENIC NOBLE GASES AND RADIONUCLIDES ON IRON METEORITES. T. Smith1, I. Leya1, S. Merchel2, G. Rugel2, S. Pavetich2, A. Wallner3, K. Fifield3, S. Tims3 and G. Korschinek4. 1University of Bern, Space Research and Planetary Sciences, Bern, Switzerland. EMail: thomas.smith@space.unibe.ch. 2Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Dresden, Germany. 3The Australian National University (ANU), Canberra, Australia. 4TU Munich (TUM), Physic Department, Germany.
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Natural plutonium from supernovae The rapid neutron capture process (r-process) produces many of the heavy chemical elements, but the astrophysical settings where it occurs remain unclear. Leading candidates are neutron star mergers and... more
Natural plutonium from supernovae The rapid neutron capture process (r-process) produces many of the heavy chemical elements, but the astrophysical settings where it occurs remain unclear. Leading candidates are neutron star mergers and some types of supernovae. Wallner et al. analyzed the plutonium content of a deep-sea crust sample, identifying a few dozen atoms of the r-process isotope plutonium- 244 that were delivered to Earth within the past few million years. There was a simultaneous signal of iron-60, which is known to be produced in supernovae. Comparing the ratios of these isotopes constrains the relative contributions of supernovae and neutron star mergers to r-process nucleosynthesis. Science , this issue p. 742
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Significance Nearby supernova explosions shape the interstellar medium. Ejecta, containing fresh nucleosynthetic products, may traverse the solar system as a transient passage, or alternatively the solar system may traverse local clouds... more
Significance Nearby supernova explosions shape the interstellar medium. Ejecta, containing fresh nucleosynthetic products, may traverse the solar system as a transient passage, or alternatively the solar system may traverse local clouds that may represent isolated remnants of supernova explosions. Such scenarios may modulate the galactic cosmic-ray flux intensity to which Earth is exposed. Varying conditions of the traversed interstellar medium could have impacts on climate and can be imprinted in the terrestrial geological record. Some radionuclides, such as 60 Fe, are not produced on Earth or within the solar system in significant quantities. Their existence in deep-sea sediments demonstrates recent production in close-by supernova explosions with a continued influx of 60 Fe until today.
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Sample preparation and AMS methodology for 99Tc have been refined with the aim of improving sensitivity to permit measurements on as little as 0.25 l of seawater. Sample preparation improvements have been directed towards minimizing 99Ru... more
Sample preparation and AMS methodology for 99Tc have been refined with the aim of improving sensitivity to permit measurements on as little as 0.25 l of seawater. Sample preparation improvements have been directed towards minimizing 99Ru and maximizing the yield of the 99TcO- ion from the ion source. A range of chemical extraction techniques and the purity of various reagents have been explored. In order to monitor the chemical yield, the gamma-emitting isotope 95mTc (T1/2=61 days), produced by the 95Mo(p,n)95Tc reaction on a natural Mo foil, was added as a tracer. On the AMS side, a new gas-filled ionization detector has been developed. This differs from that used previously in having an anode plane optimised for 99Tc, which makes eight measurements of the energy loss along the ion track. A new algorithm for maximizing the separation of 99Tc and 99Ru from the resulting multiparameter data has been developed, and allows rejection of >90% of the 99Ru ions while retaining >90% of the 99Tc counts.
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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... more
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).
Research Interests: Environmental Science, Soil, Mass Spectrometry, Australia, Accelerator Mass Spectrometry, and 14 moreBiological Sciences, Environmental Sciences, Environmental Radioactivity, Uranium, Forests, Nuclear Reactors, CHEMICAL SCIENCES, Radiation Monitoring, Southern Hemisphere, Isotope, Radioisotopes, Particle Accelerators, PLUTONIUM, and Radioactive fallout
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Research Interests: Chemistry, International Cooperation, Medicine, Seaweed, Clinical Sciences, and 12 moreRadiation Monitoring, Reproducibility of Results, Certified Reference Material, Elsevier, Sensitivity and Specificity, Radioisotopes, Reference Values, Information Value, National Institute of Standards and Technology, Applied Radiation, Reference standards, and guidelines as topic
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The beam optics of a multi-sample sputter ion source, based on the NEC MCSNICS, has been modified to accommodate cathode voltages higher than 5 kV and dispenses with the nominal extractor. The cathode voltage in Cs sputter sources plays... more
The beam optics of a multi-sample sputter ion source, based on the NEC MCSNICS, has been modified to accommodate cathode voltages higher than 5 kV and dispenses with the nominal extractor. The cathode voltage in Cs sputter sources plays the role of the classical extractor accomplishing the acceleration of beam particles from eV to keV energy, minimizing space charge effects