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Positron annihilation in off-stoichiometric and ta-doped Zn2TiO4
No full textWhile Zn vacancies are regarded as the charge compensators in Ti-rich Zn2TiO4, no evidence of cation vacancies in essentially
single-phase samples containing up to 13 wt% excess TiO2 was evident from positron annihilation lifetime spectroscopy
(PALS). Nor was there strong evidence of cation vacancies in Ta-doped samples targeted to contain either tetrahedral
or octahedral vacancies, although there was a small increase in the lifetime as the doping level increased and the structure
changed from cubic to tetragonal. © 2013, The American Ceramic Society
Technetium and ruthenium incorporation into rutile TiO2
No full textThe incorporation of TcO2 into the rutile phase of TiO2 has been theoretically examined to understand the potential of the system for use as a wasteform. The effects of defect clustering and the transmutation of Tc into Ru were considered. Results suggest that as a single defective species, Tc has a temperature-dependent, moderate solubility into rutile TiO2, which increases when clustering is considered. The {2TcTi} cluster that preferentially forms was found to have a Tc–Tc bond length similar to the cation distance in TcO2. The transmutation of Tc to Ru has two effects: first, the preferred binary cluster morphology changes from that of first nearest neighbour for {2TcTi} to that of second nearest neighbour for {2RuTi}. Second, the defect solubility is lower for single RuTi defects and Ru-containing defect clusters. This will likely result in the formation of a secondary phase as transmutation proceeds, if Tc is added to rutile TiO2 to its solution limit. The varying solubility of RuO2 in TiO2 with temperature was compared with previously published experimental data with encouraging results. The use of two different DFT codes (one plane-wave and one local-orbital) was used to find the correct magnetic ordering in the defective lattices, which increased the confidence in the methods and therefore the results. © 2013, Elsevier B.V
Chemistry and radiation effects of davidite
No full textDavidite (A1−xM21O38) samples from five different geological localities contain approximately 0.2 to 9.5 wt% UO2 (0.02 to 0.65 atoms per formula unit) and <0.1 to 1.3 wt% ThO2 (<0.01 to 0.09 atoms per formula unit). Maximum amounts of other notable cations include 3.7 wt% V2O3, 4.1 wt% Cr2O3, 2.5 wt% Y2O3, 5.6 wt% La2O3, 6.0 wt% Ce2O3, 4.0 wt% MnO, 2.4 wt% ZnO, 2.7 wt% SrO, and 4.9 wt% PbO. As a result of the variation in age and Th-U content, the calculated α decay dose ranges from ~0.2 to 44 × 1016 α/mg (~0.06 to 14.5 dpa). For samples with ages of 275–295 Ma, the critical dose for amorphization based on electron diffraction is ~0.8 × 1016 α/mg. Natural davidite is commonly altered to rutile, ilmenite, titanite, and other minor phases. © 2013, Mineralogical Society of America
Residual stress in coatings produced by cold spray
No full textCold spray technology is used to produce metal coatings with a variety of functions, including surface corrosion protection, improvement of wear resistance, etc. Cold sprayed materials exhibit a wide range of behaviours resulting in large variation of spraying efficiency, coating properties, quality and performance in service. Residual stress, being a result and attribute of the deposition process, can be studied to test whether the coating is in tension/compression stress state and also to provide information about the thermo-mechanical history of the material during the deposition process. Residual stress distributions in a variety of coating materials have been studied by neutron diffraction. Through-thickness residual stress profiles show that the stress magnitude varies significantly and depends mainly on the mechanical properties of the coating material
Synthesis of hexa aza cages, SarAr-NCS and AmBaSar and a study of their metal complexation, conjugation to nanomaterials and proteins for application in radioimaging and therapy
No full textA novel hexa aza cage, N1-(4-isothiocyanatobenzyl)-3,6,10,13,16,19-hexaazabicyclo[6.6.6]icosane-1,8-diamine (SarAr-NCS) was synthesized in good yield and characterized by 1H NMR and electrospray mass spectrometry. A new method for the synthesis of the related N1-(4-carboxybenzyl)-3,6,10,13,16,19-hexaazabicyclo[6.6.6]icosane-1,8-diamine (AmBaSar) using the p-carboxybenzaldehyde is reported. The complexation of Cu2+, Co2+ and Zn2+ by the two ligands over a range of pHs was found to be similar to the parent derivative SarAr. SarAr-NCS was conjugated to both silica particles (≈90 nm diam.) and the model B72.3 murine antibody. The SarAr-NCSN-silica particles were radiolabeled with Cu2+ doped 64Cu and the number of ligands conjugated was calculated to be an average of 7020 ligands per particle. Conjugation of SarAr-NCS to the B72.3 antibody was optimized over a range of conditions. The SarAr-NCSN-B72.3 conjugate was stored in buffer and as a lyophilized powder at 4 °C over 38 days. Its radiolabeling efficiency, stability and immunoreactivity were maintained. The development of a high yielding synthesis of SarAr-NCS should provide an entry point for a wide range of Cu and Zn radiometal PET imaging agents and potentially radiotherapeutic agents with 67Cu. © 2013, The Royal Society of Chemistry
Sequestration of atmospheric CO2 in a weathering-derived, serpentinite-hosted magnesite deposit: 14C tracing of carbon sources and age constraints for a refined genetic model
No full textThe Attunga magnesite deposit is texturally and geochemically distinct from other spatially associated, serpentinite-hosted magnesite deposits in the Great Serpentinite Belt, New South Wales, Australia, such as the hydrothermal Piedmont magnesite deposit or widespread silica–carbonate alteration zones. Cryptocrystalline magnesite at Attunga predominantly occurs in nodular masses and irregular, desiccated veins that occupy pre-existing cracks and pore spaces resulting from fracturing and weathering of the host rock. Incipient weathering of the serpentinite host rock is accompanied by a decrease in volume and the mobilisation of MgO and CaO from the serpentinite. Pore spaces and permeability created during weathering and fracturing of the host rock provide access for CO2-, MgO- and CaO-bearing meteoric waters which led to an increase of volume during carbonation. SiO2 is only mobilised during more advanced stages of weathering and late stage infiltration of SiO2-bearing waters and precipitation of opal-A lead to local silicification of the serpentinite.
Stable carbon and oxygen isotope signatures show that nodular magnesite at Attunga has formed under near-surface conditions incorporating carbon from C3-photosynthetic plants and oxygen from meteoric waters. Radiocarbon concentrations in the magnesite preclude subducted carbonaceous sediments as the source of carbon and, together with distinct stable carbon and oxygen isotope signatures, indicate that magnesite at Attunga precipitated from low temperature, supergene fluids. Even though there is no direct geochemical and isotopic evidence, some textural observations and field relationships for weathering-derived magnesite deposits suggest the prior existence of a possibly Early Triassic, hydrothermal magnesite deposit at Attunga. The presence of a pre-existing magnesite deposit may entail the localised formation of the weathering-derived magnesite at Attunga, but the predominance of weathering-related textures and geochemical signatures indicate that weathering is the integral magnesite mineralisation process at Attunga. Conventional radiocarbon ages of about 50 ka represent a maximum age constraint for the formation of the magnesite deposit during Quaternary weathering. A significant amount of atmospheric CO2 has been sequestered via the biosphere and carbonation of serpentinite at Attunga. © 2013, Elsevier Ltd
Crystal structure and phase transitions in the uranium perovskite, Ba2SrUO6
No full textThe structure of one of the oxides proposed to be present in the grey phase of irradiated mixed oxide fuel, the double perovskite Ba2SrUO6 has been investigated from room temperature to 1300 K using synchrotron X-ray powder diffraction methods. The divalent strontium and hexavalent uranium are found to be fully ordered in the double-perovskite arrangement of alternating octahedra sharing corner oxygen atoms. At room temperature Ba2SrUO6 adopts a monoclinic structure in space group P21/n. Heating to above 900 K induces a first order transition to a rhombohedral structure, and further heating to above
1200 K results in a continuous transition to a cubic structure. The sequence of structures is associated with the progressive loss of cooperative tilting of the corner sharing SrO6 and UO6 octahedra.
© 2012, Elsevier B.V
Lake Carpentaria
No full textThe modern drainage catchment of the Gulf of Carpentaria (Figure 9.2) comprises more than 25 monsoon-fed rivers that collectively provide 25% of the total fluvial run-off of the Australian continent (Figure 9.12). The Gulf is bounded to the east by Torress Strait(maximum water depth 12m) and by the Arafura Sill (water depth 53 m) to the west. The deepest, eastern central portion of the Gulf today is 71 m (Figure 9.13). Accordingly, during episodes of low Quaternary sea levels, the Gulf was separated from the open waters of the Indian and Pacific Oceans and formed the large freshwater-brackish Lake Carpentaria (Torgersen et al. 1983, 1985, 1988; Jones & Torgersen 1988). When most recently filled, the lake had a maximum depth of 15-18m and the lateral dimensions of about 600 x 300K, with overflow westwards into the Arafura Sea (Chivas et al. 2001). Among modern lakes, only the Caspian Sea has a larger surface area. Throughout the past glacial cycle of -125 000 years, there was at least one land bridge between Australia and New Guinea for more than 90% of this time. © 2013, Queensland Government
Radiocarbon applications in environmental and earth sciences
No full textRadiocarbon or 14C is one of the most important cosmogenic radionuclides for
building reliable chronologies for various materials and archives for the study of
environmental and climatic changes for the past 50 ka. Radiocarbon is also used as a
powerful tracer of the carbon cycle and climatic systems. After a short discussion on recent advances in accelerator mass spectrometry (AMS) 14C analysis, this paper highlights several applications of radiocarbon in earth and environmental sciences that have been carried out at ANSTO.AINSE, Sercon, GNS Science, Thermo Fisher Scientific, Isoprime, nu instruments
Plutonium transfer to wildlife at legacy sites
Get PDFWhen internalized within an organism’s body, plutonium (Pu) can be important in dose calculation due to its relatively high-energy alpha emissions (~5-6 MeV). In this paper we quantify transfer of Pu to a range of wildlife types at legacy nuclear weapons sites and evaluate the importance of body tissue Pu distribution in the transfer of Pu through the food chain. The paper presents new data from Maralinga, Australia, as well as past data from terrestrial and marine settings of the US nuclear research program