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Stable platinum isotope measurements in presolar nanodiamonds by TEAMS
No full textNanodiamonds are stardust grains commonly found in primitive meteorites. They survived the formation of the solar system and kept their own individuality. Measurements of trace-element isotopic signatures
in these grains will help understanding heavy element nucleosynthesis in massive stars and dust formation from their ejecta. We have continued previous attempts to search for stable Pt isotope anomalies in
nanodiamonds via trace element accelerator mass spectrometry (TEAMS). The installation of a new injector beam line at the VERA facility allowed studying low traces of stable elements in different materials.
Moreover, recent experiments showed that VERA provides the required measurement precision together with a low Pt machine background. Here, we observed for the first time an indication for enhancements
of 198Pt/195Pt isotope ratios in two diamond residues prepared by different chemical separation techniques
from the Allende meteorite. Variations in other isotopic ratios were within analytical uncertainty, and no anomaly was identified in a third diamond fraction. © 2012, Elsevier B.V
Development activities in the accerlerator operations group development task
Get PDFThe Operations Group Development team within the ANSTO Accelerator facilities are currently persuing a number of activities to further develop our equipment and technical capabilities.
These include broadly;
*Electron Cyclotron Resonance Ion Sources
(ECRIS)
* Virtual Instrumentation
* Beam Profile Monitor Enhancements
* Vacuum System Operation Methods
* Current Digitisers/Integrator
Choosing the right stripper gas from AMS and other applications with tandem accelerators at low and medium terminal voltage
Get PDFRecent experimentation with stripper gases used for Accelerator Mass Spectrometry (AMS)
has seen a divergence in the practices adopted at laboratories performing AMS of high mass species (such as actinides) at low and medium terminal voltages. At low voltages (<1 MV), the Ion Beam Group at ETH Zurich has demonstrated the advantages of using helium as the stripper gas, for both radiocarbon AMS [1] and for actinides AMS [2]. Meanwhile, at ANSTO we have investigated several gases at 4 MV [3, 4] and find that a multi–atom molecular gas
such as sulphur hexafluoride provides the best yield for actinides AMS. In both cases, data published 40 years ago provided clues as to the optimum gas in each situation
The geological trace of the 1932 tsunamis in the tropical Jalisco-Colima
No full textThe study and preservation of tsunami deposits have being challenging in humid tropical environments. While tsunami deposits have been widely studied at temperate latitudes, few studies assess this problem in tropical environments due to the difficulties intrinsic to these places (e.g. tsunami deposit preservation, post-burial changes in a tropical environment, mangrove vegetation, difficult access, wildlife, among others). Here we assess the problem of tsunami-deposits preservation on the Jalisco-Colima tropical coast of Mexico, which parallels the more than 1000-km long Mexican subduction, where historical accounts indicate the occurrence of two significant tsunamis on June 3 and 22, 1932 (Corona and Ramírez-Herrera, 2012a, Valdivia et al., 2012). However, up to date, no geological evidence of these events has been reported. We present geological evidence of two large tsunamis related to the June 3, M 8.2 earthquake, and the June 22, Ms 6.9 landslide-triggering event of 1932 (Corona and Ramírez-Herrera, 2012a, b). A multiproxy approach was applied to unravel the nature of anomalous sand units and sharp basal contacts in the stratigraphy of a number of sites at Palo Verde estuary, El Tecuán swales and marsh, and La Manzanilla swales, on the Jalisco-Colima coast. Lines of evidence including historical, geomorphological, stratigraphic, grain size, organic matter content, microfossils (diatoms and foraminifera), geochemical content, magnetic susceptibility and AMS analyses, together with dating (210Pb and 14C), and modeling, corroborate the presence of tsunami deposits of both the 3 June 1932 tsunami at El Tecuán and La Manzanilla, and the 22 June 1932 tsunami at Palo Verde. Further evidence of earlier tsunamis, at least four events, is also evident in the stratigraphy. Work in progress should reveal the chronology of the earliest tsunamis and their origin. Corona, N., M.T. Ramirez-Herrera. (2012a) Mapping and historical reconstruction of the great Mexican 1932 tsunami. Natural Hazards and Earth System Sciences, 12, 1337-1352. NHESS-2011-369. Corona Morales N. y M.T. Ramírez-Herrera. (2012b) Técnicas histórico-etnográficas en la reconstrucción y caracterización de tsunamis: El ejemplo del gran tsunami del 22 de junio de 1932, en las costas del Pacífico Mexicano. Revista de Geografía Norte Grande. 53, 107-122. Valdivia O. L., Castillo A. M.R., Trejo E. M. (2012). Tsunamis en Jalisco, Geocalli, Cuadernos De Geografía, Universidad de Guadalajara. Año 13, No. 25, 103p
Flood-flipped boulders: in-situ cosmogenic nuclide modeling of flood deposits in the monsoon tropics of Australia
No full textDuring the Quaternary, extreme floods along the Durack River, in the Kimberley, northern Australia, dislodged, transported, and stacked massive meter-sized boulders from the underlying bedrock channel floor. Field evidence identified a population of the boulders to have been overturned after detachment. We measured in situ cosmogenic 10Be and 26Al concentrations in six imbricated boulders to constrain the timing of flood events. We present a simple numerical model that simultaneously solves the expressions for the predicted nuclide concentrations from the exposed and hidden surfaces of a flipped boulder to calculate the time since it was overturned. The ability of the model to unequivocally discern whether a boulder was overturned depends on boulder thickness and the site-specific steady-state erosion rate. Of the six boulders sampled, our model successfully determined four finite flip ages, whereas the other two boulders indicated steady state and were either not flipped or flipped sufficiently long ago for the nuclide profile to have returned to steady state. While the two older model ages (ca. 150 ka and ca. 260 ka) are strongly sensitive to assumptions made for the local erosion rate correction, the two younger flip ages, 5.6 ± 1.0 ka and 10.3 ± 1.9 ka, are robust against such corrections. Early to mid-Holocene major floods have been recorded in other parts of northern Australia. We suggest that similar Holocene floods occurred in the Kimberley and that such extreme events may have been widespread in northern Australia in the late Quaternary. Our boulder-flip model can be applicable to similar deposits associated with other extreme events such as paleo-tsunamis. © 2014, Geological Society of America
21Ne, 10Be and 26Al cosmogenic burial ages of near-surface eolian sand from the Packard Dune field, McMurdo Dry Valleys, Antarctica.
No full textThe McMurdo Dry Valleys, Antarctica, have been ice-free for at least 10 Ma. In Victoria Valley, the largest of the
Dry Valleys, permafrosted yet still actively migrating dune-fields, occupy an area of 8 km2 with dune thicknesses
varying from 5 to 70 meters. High-resolution ground penetrating radar (GPR) imaging of selected dunes reveal
numerous unconformities and complex stratigraphy inferring cycles of sand accretion and deflation from westerly
katabatic winter winds sourced from the East Antarctic Ice Sheet and anabatic summer winds sourced from the
Ross Sea. Samples above permafrost depth were taken for OSL and cosmogenic 26Al/10Be burial ages. OSL ages
from shallow (<1m) pits range from modern to 1.3ka suggesting that deposition/reworking of the dunes is ongoing
and their present configuration is a late Holocene feature. The same 7 samples gave a mean 26Al/10Be = 4.53
+/- 5% with an average apparent continuous 10Be surface exposure age of 525 +/- 25 ka surprisingly indicating
a common pre-history independent of depth. Correcting for minor post-burial production based on OSL ages, the
minimum (integrated) burial period for these sand grains is 0.51+/- 0.12 Ma which represents the burial age at the
time of arrival at the dune. A possible explanation is that this common burial signal reflects recycling episodes
of exposure, deposition, burial and deflation, sufficiently frequent to move all grains towards a common pre-dune
deposition history. However, it is unclear over what length of time this processes has been active and fraction of
time the sand has been buried. Consequently we also analysed purified quartz aliquots of the same samples for a
third and stable nuclide, 21Ne, to determine the total surface and burial exposure periods. Using the 21Ne/10Be
system we obtain burial ages of 1.10 +/- 0.10 Ma. Further coring below permafrost is planned for austral summer 2015. © Copyright, 2015 XIX INQUA Congress LOC
Facile synthesis of reduced graphene oxide/MWNTs nanocomposite supercapacitor materials tested as electrophoretically deposited films on glassy carbon electrodes
Get PDFThis paper reports on a facile synthesis method for reduced graphene oxide (rGO)/multi-walled carbon nanotubes (MWNTs) nanocomposites. The initial step involves the use of graphene oxide to disperse the MWNTs, with subsequent reduction of the resultant graphene oxide/MWNTs composites using l-ascorbic acid (LAA) as a mild reductant. Reduction by LAA preserves the interaction between the rGO sheets and MWNTs. The dispersion-containing rGO/MWNTs composites was characterized and electrophoretically deposited anodically onto glassy carbon electrodes to form high surface area films for capacitance testing. Pseudo capacitance peaks were observed in the rGO/MWNTs composite electrodes, resulting in superior performance with capacitance values up to 134.3 F g−1 recorded. This capacitance value is higher than those observed for LAA-reduced GO (LAA-rGO) (63.5 F g−1), electrochemically reduced GO (EC-rGO) (27.6 F g−1), or electrochemically reduced GO/MWNTs (EC-rGO/MWNTs) (98.4 F g−1)-based electrodes.© 2013, Springer Science+Business Media Dordrecht
Non-injection synthesis of Cu2ZnSnS4 nanocrystals using a binary precursor and ligand approach
No full textWe present a non-injection, one-pot synthesis of kesterite Cu2ZnSnS4 (CZTS) nanocrystals (NCs) that allows for multi-gram
yields with precise control of the NCs’ metal composition. This is enabled through the selective use of a binary sulfur precursor and ligand reaction mixture, which acts to decouple the nucleation and growth stages. © 2013, The Royal Society of Chemistry
Coexistence of long-range magnetic ordering and singlet ground state in the spin-ladder superconductor SrCa13Cu24O41
No full textA long-range magnetic order was discovered in the quasi-one-dimensional spin-ladder compound SrCa13Cu24O41 by susceptibility, specific heat, and neutron diffraction experiments. The temperature dependence of the magnetic Bragg peak intensity could be well fitted to the power law with a transition temperature TN = 4.23 K and a critical exponent β = 0.28, indicating a three-dimensional phase transition for a low-dimensional magnet. A computer program was coded and found two possible magnetic structure models fitting best with all the observed magnetic peaks. These models suggest the spin-ladder sublattice is magnetically ordered with Cu moments aligning along the a axis. The spin interactions are primarily antiferromagnetic along rungs and legs, while there are ferromagnetic clusters along legs. Surprisingly, the singlet-triplet spin-gap excitation is observable above and below TN, indicating a coexistence of the spin-singlet ground state and long-range magnetic ordering state in this compound. © 2013, American Physical Society