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Interpreting past climate using southwest Australian speleothems
No full textThere is an identified need to extend our baseline climate information beyond the relatively short duration of
instrumental records in Australia. An improved knowledge of natural rainfall variability would assist in our understanding of climate change. SW Australia (SWWA) is one region that has been identified as having a
changing climate since the 1970s.
Speleothems (cave stalagmites) are an effective archive of past climate variability and caves from the coastal
region of SWWA are being studied for paleoclimate records. The modern speleothem record from this region
has been assessed and shown to record the post-1970s rainfall decrease (Treble et al., 2003; 2005; Fischer
and Treble, 2008). The extension of the speleothem record is currently underway, however, a long-term cave
monitoring program was also deemed necessary to separate the climatic from non-climatic signals i.e. to
reduce uncertainty when interpreting these records.
This presentation outlines what we have learnt about the possible hydrological modification of the climate
signal in speleothems. In particular, we present results from a five-year long monitoring study of rainfall and
cave drip water O isotopes (!18O) from Golgotha Cave, SWWA. From this study, we have been able to
characterize the probable flow paths feeding stalagmites in our monitored cave. These flow paths range from
slow diffuse flow of isotopically-averaged rainfall to preferential routing of high-magnitude, 18O-depleted,
events along fast flow routes into the cave. Hence, we offer a possible explanation for why paleoclimate
records from coeval speleothems in our cave may differ. Our study suggests that this disagreement may
simply be due to different flow paths resulting in a bias towards the preservation of high or low magnitude
rainfall events
Six problems with the 6-day Curie and a solution
No full textIn this review the major shortfalls of the unit of sale for the Mo-99 supply chain—the 6-day Curie—are identified and discussed. These include its status as an inconsistent, out-dated, non-SI unit, and its use causing propagation of inefficient logistics within the Mo-99 supply chain. An alternative Mo-99 unit of sale is proposed: Becquerels time-stamped at the Port of Despatch. Adoption of the new unit is proposed as a catalyst in the move away from the current economically unsustainable, Mo-99 supply chain in favour of simplicity, self-regulation, transparency, efficiency, and full-cost recovery in line with High-Level Group for the Security of Supply of Medical Radioisotopes recommendations. © 2020 Springer Nature Switzerland A
High-sensitivity isobar-free AMS measurements and reference materials for 55Fe, 68Ge and 202gPb
No full textIsobaric interference represents one of the major limitations in mass spectrometry. For a few cases in AMS with tandem accelerators, isobaric interference is completely excluded like the well-known major isotopes 14C, 26Al, 129I. Additional isotopes are 55Fe (t1/2=2.74years), 68Ge (t1/2=270.9days) and 202Pb (t1/2=52.5kyr), with 68Ge and 202Pb never been used in AMS so far. Their respective stable isobars, 55Mn, 68Zn and 202Hg do not form stable negative ions. The exceptional sensitivity of AMS for 55Fe, 68Ge and 202gPb offers important insights into such different fields like nuclear astrophysics, fundamental nuclear physics and technological applications. VERA, a dedicated AMS facility is well suited for developing procedures for new and non-standard isotopes. AMS measurements at the VERA facility established low backgrounds for these radionuclides in natural samples. Limits for isotope ratios of <10−15, <10−16 and ⩽2×10−14 were measured for 55Fe/56Fe, 68Ge/70Ge and 202Pb/Pb, respectively. In order to generate accurate isotope ratios of sample materials, AMS relies on the parallel measurement of reference materials with well-known ratios. A new and highly accurate reference material for 55Fe measurements with an uncertainty of ±1.6% was produced from a certified reference solution. In case of 68Ge dedicated neutron activations produced a sufficiently large number of 68Ge atoms that allowed quantifying them through the activity of its decay product 68Ga. Finally, for 202Pb, the short-lived isobar 202Tl was produced via neutron activation and served as a proxy for 202Pb AMS measurements. © 2012 Elsevier B.V
Neutron diffraction strain tomography: Demonstration and proof-of-concept
No full textRecently, a number of reconstruction algorithms have been presented for residual strain tomography from Bragg-edge neutron transmission measurements. In this paper, we examine whether strain tomography can also be achieved using diffraction instruments. We outline the proposed method and develop a suitable reconstruction algorithm. This technique is demonstrated in simulation, and a proof-of-concept experiment is carried out, where the strain field in an axisymmetric sample is reconstructed and validated using conventional diffraction strain scans. © 2020 AIP Publishing LLC
Gapless spin liquid in a square-kagome lattice antiferromagnet
Get PDFObservation of a quantum spin liquid (QSL) state is one of the most important goals in condensed-matter physics, as well as the development of new spintronic devices that support next-generation industries. The QSL in two dimensional quantum spin systems is expected to be due to geometrical magnetic frustration, and thus a kagome-based lattice is the most probable playground for QSL. Here, we report the first experimental results of the QSL state on a square-kagome quantum antiferromagnet, KCu6AlBiO4(SO4)5Cl. Comprehensive experimental studies via magnetic susceptibility, magnetisation, heat capacity, muon spin relaxation (μSR), and inelastic neutron scattering (INS) measurements reveal the formation of a gapless QSL at very low temperatures close to the ground state. The QSL behavior cannot be explained fully by a frustrated Heisenberg model with nearest-neighbor exchange interactions, providing a theoretical challenge to unveil the nature of the QSL state. © 2020 Springer Nature Limite
High proton conductivity in Ba5Er2Al2ZrO13, a hexagonal perovskite-related oxide with intrinsically oxygen-deficient layers
No full textFor the development of proton-based electrolytes, high proton conductivity at intermediate temperatures (300–600 °C) is crucial, but the available materials have been confined to a limited number of the structure families, such as cubic perovskites. Herein, we report Ba5Er2Al2ZrO13, a hexagonal perovskite-related oxide, as a new class of proton conductors exhibiting higher conductivities than 10–3 S cm–1 between 300 and 1200 °C. The protons as charge carriers are found to exist in the inherently oxygen-deficient h′ layer of Ba5Er2Al2ZrO13, which are supported by Rietveld analysis of neutron-diffraction data, bond-valence-based energy calculations, and thermogravimetric analysis. Our discovery of a new structure family of proton conductors with the inherently oxygen-deficient h′ layer offers a strategy in designing superior proton conductors based on hexagonal perovskite-related oxides. © 2020
American Chemical Societ
Silver nanoparticles prepared by gamma irradiation across metal organic framework templates
No full textIn this study, we demonstrate for the first time the successful fabrication of well-dispersed ultrafine silver nanoparticles inside metal–organic frameworks through a single step gamma irradiation at room temperature. HKUST-1 crystals are soaked in silver nitrate aqueous solution and irradiated with a Cobalt 60 source across a range of irradiation doses to synthesize highly uniformly distributed silver nano-particles. The average size of the silver nanoparticles across the Ag@HKUST-1 materials is found to vary between 1.4 and 3 nm for dose exposures between 1 and 200 kGy, respectively. The Ag@HKUST-1 hybrid crystals exhibit strong surface plasmon resonance and are highly durable and efficient catalytic materials for the reduction of 4-nitrophenol to 4-aminophenol (up to 14.46 × 10−3 s−1 for 1 kGy Ag@HKUST-1). The crystals can be easily recycled for at least five successive cycles of reaction with a conversion efficiency higher than 99.9%. The gamma irradiation is demonstrated to be an effective and environmental friendly process for the synthesis of nano-particles across confined metal–organic frameworks at room temperature with potential applications in environmental science. © 2015 The Royal Society of Chemistr
Solvent extraction of rare earth elements using phosphonic/phosphinic acid mixtures
No full textThis work examines the extraction of rare earths (Ce, Pr, Nd, Sm, Tb, Dy, Ho, Er, Yb, Lu and Y) by 2-ethylhexyl phosphonic acid 2-ethylhexyl mono-ester (EHEHPA), Cyanex 272, Cyanex 572 and mixtures of EHEHPA and Cyanex 272, to determine whether the mixed extractants could be beneficial to industrial rare earth separations. Analysis of the effect of pH and extractant concentration on distribution ratios indicated that addition of the phosphinic acid to EHEHPA resulted in an antagonistic effect. The antagonistic effect was confirmed using the method of continuous variation, and is thought to be due to an association between the phosphinic and phosphonic acids which reduces the free dimer concentrations of each component. Examination of 31P{1H} NMR spectra showed that for the mixed extractant the extracted yttrium complex was predominantly composed of EHEHPA. However, some Cyanex 272 was also found to be associated with yttrium, which suggests the formation of a mixed yttrium–EHEHPA–Cyanex 272 complex. Separation factors for the mixed extractants were similar to those of EHEHPA, while the maximum loading for equimolar extractants was approximately halved. The results suggest potential savings resulting from a reduction in the stripping acid required for the mixed extractant relative to equimolar EHEHPA; however equipment size would likely increase due to lower overall metal loading. © 2015 Elsevier B.V
Structural changes from native waxy maize starch granules to cold-water sluble phrodextrin during thermal treatment
No full textThe structural changes occurring during the thermal conversion of insoluble native waxy maize starch granules to cold-water-soluble pyrodextrin under acidic conditions have been investigated by multiple techniques, including synchrotron small-angle X-ray scattering (SAXS), wide-angle X-ray scattering, differential scanning calorimetry, and gel permeation chromatography. In a mixture of water/glycerol (20/80, w/w), the SAXS characteristic peak at ca. 0.6 nm–1 decreased in intensity as pyrodextrin solubility increased. The peak disappeared as pyrodextrin solubility reached 100%. Starch crystal size, its associated melting enthalpy, and pyrodextrin molecular size decreased as solubility increased. Although starch structure changed during thermal conversion, the pyrodextrins appeared identical to the native starch when observed in glycerol under a normal and polarized light microscope. It is proposed that the starch backbone is hydrolyzed by acid in the amorphous region and the crystalline region with starch molecules being hydrolyzed into small molecular fractions but persisting in a radial arrangement. © 2020
American Chemical Societ
Paleoclimate studies and natural-resource management in the Murray-Darling Basin II: unravelling human impacts and climate variability
No full textThe management of the water resources of the Murray-Darling Basin (MDB) has long been contested, and the effects of the recent Millennium drought and subsequent flooding events have generated acute contests over the appropriate allocation of water supplies to agricultural, domestic and environmental uses. This water-availability crisis has driven demand for improved knowledge of climate change trends, cycles of variability, the range of historical climates experienced by natural systems and the ecological health of the system relative to a past benchmark. A considerable volume of research on the past climates of southeastern Australia has been produced over recent decades, but much of this work has focused on longer geological time-scales, and is of low temporal resolution. Less evidence has been generated of recent climate change at the level of resolution that accesses the cycles of change relevant to management. Intra-decadal and near-annual resolution (high-resolution) records do exist and provide evidence of climate change and variability, and of human impact on systems, relevant to natural-resource management. There exist now many research groups using a range of proxy indicators of climate that will rapidly escalate our knowledge of management-relevant, climate change and variability. This review assembles available climate and catchment change research within, and in the vicinity of, the MDB and portrays the research activities that are responding to the knowledge need. It also discusses how paleoclimate scientists may better integrate their pursuits into the resource-management realm to enhance the utility of the science, the effectiveness of the management measures and the outcomes for the end users. © 2020 Informa UK Limite