Initial results and observations on a radiocarbon dating program in the Riverland region of South Australia

This paper presents a preliminary occupation chronology for the Riverland region of South Australia, based on 31 radiocarbon age determinations. This region has represented a significant geographic gap in understanding occupation chronologies for the broader Murray-Darling Basin. The dating forms part of an ongoing research program exploring the long-term engagements of Aboriginal people with the habitat mosaics of the central River Murray corridor. Dating targets were selected on the basis of their landscape context. Results relate occupation evidence to an evolving riverine landscape through the period extending from approximately 29 ka to the late Holocene. These results include the first pre-Last Glacial Maximum ages returned on the River Murray in South Australia and extend the known Aboriginal occupation of the Riverland by approximately 22,000 years. © 2020 Informa UK Limite

Determination of niobium diffusion in titania and zirconia using secondary ion mass spectrometry

This paper provides an outline for the use of secondary ion mass spectrometry (SIMS) in the determination of diffusion data in metal oxides. The focus is on the determination of Nb bulk and grain boundary diffusion coefficients in TiO2 and zirconia. Specifically, the diffusion of Nb in TiO2 and yttria doped (10 mol.-%) ZrO2 (10YSZ) has been assessed. The following bulk diffusion coefficients D 93Nb were obtained D 93Nb =(1·03±0·051) × 10−18 m2 s−1 10YSZ(1273K) D 93Nb =(1·91±0·096) × 10−16 m2 s−1 TiO2(1273K) The grain boundary diffusion parameter for Nb grain boundary diffusion in 10YSZ was also determined D 93Nb δα =(7·48 ± 0·37) × 10−25 m2 s−1 10YSZ(1273K) The Nb grain boundary diffusion coefficient D′93Nb was determined to be D′93Nb =(3·99 ± 0·20) × 10−16 m2 s−1 10YSZ(1273K)© 2007 Informa UK Limite

Optimisation of [11C]raclopride production using a synthra GPextent system

The dopamine D2 receptor radiotracer [(11)C]Raclopride is used extensively in clinical and preclinical imaging. Currently, a wide range of methods to produce [(11)C]Raclopride have been developed using traditional vessel reactions as well as cartridge or captive solvent. This work reports the optimisation of the production of [(11)C]Raclopride using a Synthra GPextent, comparing various methods. With optimised conditions, we were able to obtain 4±2% (ndc) yield of [(11)C]Raclopride (100 GBq [(11)C]CO2, n = 42) in 25 min. The radiochemical purity was >95% with specific activities of 135±41 MBq/nmol at end of synthesis. © 2014 Bentham Science Publisher

Solvent extraction of rare earth elements using phosphonic/phosphinic acid mixtures

This 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

Pyrochlore glass‐ceramics fabricated via both sintering and hot isostatic pressing for minor actinide immobilization

Pyrochlore glass‐ceramics (GCs) have been investigated with samples fabricated via both sintering and hot isostatic pressing (HIPing) of a mixed oxide precursor. It has been demonstrated that sintering at 1200°C in air is necessary to obtain well‐crystallized pyrochlore crystals in a sodium aluminoborosilicate glass through a one‐step controlled cooling. The crystallization, structure, and microstructure of Eu2Ti2O7 pyrochlore as the major phases in residual glass were confirmed with X‐ray diffraction (XRD), scanning electron microscopy‐energy dispersive spectroscopy, transmission electron microscopy, and Raman spectroscopy. The structures of major Eu2Ti2O7 pyrochlore and minor [Eu4.67O(SiO4)3] apatite in both sintered and HIPed samples were refined using synchrotron XRD data. While the processing atmosphere did not appear to affect the cell parameter of the main pyrochlore phase, very small volume expansion (~0.3%) was observed for the minor apatite phase in the HIPed sample. In addition, static leaching of the HIPed sample confirmed that pyrochlore GCs are chemically durable. Overall, pyrochlore GCs prepared via both sintering and HIPing with the Eu partitioning factor of ~23 between ceramics and the residual glass are suitable waste forms for minor actinides with processing chemicals. © 1999-2020 John Wiley & Sons, Inc

Mössbauer study of the temperature dependence of electron delocalization in mixed valence freudenbergite

The evolution of the electron delocalization in the ferrous subspectra in a sample of mixed valence ferrous‐ferric freudenbergite has been followed by Mössbauer spectroscopy from 6 K to 650 K. The spectral changes do not involve the ferric component, leading to the conclusion that it is due to a thermally driven delocalization of the sixth d‐electron on the ferrous ions. The phenomenon does not occur in samples of pure ferrous freudenbergite. © 1999-2020 John Wiley & Sons, Inc

Mercury vapor sensor enhancement by nanostructured gold deposited on nickel surfaces using galvanic replacement reactions

Anthropogenic mercury emission is a serious global environmental problem because of its toxicity to humans, plants and wildlife. In order to control these emissions, accurate and reliable online continuous mercury monitoring systems (CMMs) are critical. Such systems can notify appropriate authorities or provide feedback signals to a process control system in time, thus making them an integral part of monitoring and controlling Hg emissions. We demonstrate how nanostructured gold can easily be deposited in small quantities on nickel electrode based QCMs using galvanic replacement (GR) reactions with the resultant surface having excellent Hg monitoring properties. The developed GR surfaces were observed to have higher sensitivity and selectivity in the presence of interfering gas species (NH3 and H2O), as well as to have ∼80% higher mercury sorption capacity than the most efficient mercury sorbents reported to date. Investigations towards the Hg-sensing capabilities of the resultant Ni–Au surface based Hg sensors showed ∼50% better sensitivity and detection limit over control Au films. Furthermore, the GR based QCMs were found to self-regenerate without changing the operating temperature of the sensor, undergoing Hg desorption with sensor recoveries of 93.7–99.3% following Hg exposure at an operating temperature of 90 °C. Surface depth profile analysis of the Ni–Au electrode surfaces showed that the high recovery rate of the sensors was primarily due to the Ni–Au structures, which unlike continuous Au thin-films more commonly used for Hg sensing applications, do not accumulate Hg at the sensitive-layer–substrate interface. Furthermore, the GR Ni–Au surfaces were found to be highly selective towards Hg vapor in the presence of NH3 and H2O interfering gas species which makes them potentially suitable for operating in harsh industrial effluent environments.© The Royal Society of Chemistry 201

Effect of grain size on Hertzian contact damage in 9 mol% Ce-TZP ceramics

The Hertzian contact damage in 9 mol% Ce-TZP ceramics with different grain sizes has been investigated. Single-cycle tests were conducted on materials of four grain sizes, 1.1, 1.6, 2.2 and 3 μm. The indentation stress–strain curves for all materials show striking nonlinearity and deviation from the Hertzian elastic response, illustrating a significant quasi-plastic component in the contact damage response. Subsurface damage patterns for these four materials are compared and contrasted using a bonded-interface sectioning technique. The transformation and deformation behaviour, characterised using optical and scanning electron microscopy, of the surface and subsurface regions revealed extensive deformation and compression-driven subsurface damage in the materials. Acoustic emission was used as a complementary technique in order to identify the damage processes during a load–unload cycle. Contact deformation and radial bands extending from the indent impressions due to autocatalytic tetragonal–monoclinic transformation are evident in all except the finest grained (1.1 μm) material. Irrespective of grain size there is no evidence of ring or cone cracking with all material showing hemispherical subsurface damage or yield zones resulting from the stress-induced tetragonal–monoclinic (t–m) transformation with extensive distributed microcracking within these areas for the 1.6, 2.2 and 3 μm grain-size materials. © 2002 Elsevier Science Lt

Constraining the sources of the CH4 increase during the Oldest Dryas-Bølling abrupt warming event using 14CH4 measurements from Taylor Glacier, Antarctica

Methane (CH4) is an important greenhouse gas with both natural and anthropogenic sources. Understanding how the natural CH4 budget has changed in response to changing climate in the past can provide insights on the sensitivity of the natural CH4 emissions to the current anthropogenic warming. Low latitude wetlands are the largest natural source of CH¬4 to the atmosphere. It has been proposed, however, that in the future warming world emissions from marine CH4 clathrates and Arctic permafrost might increase significantly. CH4 isotopes from ice cores in Greenland and Antarctica have been used to constrain the past CH¬4 budget. 14CH4 is unique in its ability to unambiguously distinguish between “old” CH4 sources (e.g. marine clathrate, geologic sources, old permafrost) and “modern” CH4 sources (e.g. tropical and boreal wetlands). We have successfully collected six large volume (~1000 kg) samples of ancient ice from Taylor Glacier, Antarctica that span the Oldest Dryas – Bølling (OD-BO) CH4 transition (~14.5ka). The OD-BO is the first large abrupt CH4 increase following the Last Glacial Maximum, with atmospheric CH4 increasing by ≈30% in the span of ≈ 200 years. All samples have recently been successfully measured for 14CH4, δ13C-CH4, and δD-CH4. 14CH4 measurements of accompanying procedural blanks show that effects from extraneous carbon addition during processing are small. Results are currently undergoing corrections for in-situ cosmogenic 14C based on 14CO measurements in the same samples. We will present the corrected 14CH4 results and preliminary interpretation with regard to causes of the OD-BO CH4 increase

Methane simulations at Cape Grim to assess methane flux estimates for South East Australia

A transport model intercomparison for methane (TransCom-CH4) has been run involving twelve models (Patra et al., 2011). We contributed simulations using two climate models, CCAM and ACCESS. The CCAM simulations were nudged to NCEP analysed meteorology, which allows simulated atmospheric concentrations to be compared to observations on synoptic timescales. The ACCESS simulations were forced only with observed sea surface temperatures and are consequently not expected to match observed synoptic variations. The TransCom experiment involved simulating six CH4 tracers (with different prescribed fluxes) along with SF6, radon and methyl chloroform. We have analysed hourly model output for Cape Grim and find that the magnitude of the non-baseline signal differs, especially in winter, dependent on the CH4 flux scenario used. The magnitude of the non-baseline signal also varies between models, although these differences can be reconciled when methane is scaled by model-simulated radon concentration. Comparison with observed CH4, also scaled using radon, suggests that the CH4 flux scenario with little or no wetland emissions in winter matches the observations. The observations also indicate an apparent extra source of CH4 in October-November not seen in the model simulations. However this appears to be an artefact of this analysis method which assumes that radon emissions are known (and in this case constant in space and time). We have found that the discrepancy between model and observations in spring appears to be due to a poor simulation of radon, rather than CH4. Observed radon shows a larger seasonality than modelled radon, which suggests that temporal and spatial variations in radon flux need to be considered. It would also be helpful to understand why the simulated CCAM and ACCESS radon (and non-baseline CH4) concentrations differ in magnitude. Comparisons with Cape Grim output from the other participating TransCom-CH4 models may provide some insight