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A neutron diffraction investigation of residual stresses in rail ends after severe deformation of rail surfaces
No full textInsulated rail joints (IRJs) are a primary component of the rail track safety and signalling systems. Rails are supported by two fishplates which are fastened by bolts and nuts and, with the support of sleepers and track ballast, form an integrated assembly. IRJ failure can result from progressive defects, the propagation of which is influenced by residual stresses in the rail. Residual stresses change significantly during service due to the complex deformation and damage effects associated with wheel rolling, sliding and impact. IRJ failures can occur when metal flows over the insulated rail gap (typically 6-8 mm width), breaks the electrically isolated section of track and results in malfunction of the track signalling system. In this investigation, residual stress measurements were obtained from rail-ends which had undergone controlled amounts of surface plastic deformation using a full scale wheel-on-track simulation test rig. Results were compared with those obtained from similar investigations performed on rail ends associated with ex-service IRJs. Residual stresses were measured by neutron diffraction at the Australian Nuclear Science and Technology Organisation (ANSTO). Measurements with constant gauge volume 3x3x3 mm3 were carried in the central vertical plane on 5mm thick sliced rail samples cut by an electric discharge machine (EDM). Stress evolution at the rail ends was found to exhibit characteristics similar to those of the ex-service rails, with a compressive zone of 5mm deep that is counterbalanced by a tension zone beneath, extending to a depth of around 15mm. However, in contrast to the ex-service rails, the type of stress distribution in the test-rig deformed samples was apparently different due to the localization of load under the particular test conditions. In the latter, in contrast with clear stress evolution, there was no obvious evolution of d0. Since d0 reflects rather long-term accumulation of crystal lattice damage and microstructural changes due to service load, the loading history of the test rig samples has not reached the same level as the ex-service rails. It is concluded that the wheel-on-rail simulation rig provides the potential capability for testing the wheel-rail rolling contact conditions in rails, rail ends and insulated rail joints
Oxygen Nonstoichiometry in (Ca2CoO3)0.62(CoO2): A combined experimental and Computational Study
No full textThe oxygen nonstoichiometry in the misfit calcium cobaltite (Ca2CoO3)0.62(CoO2) has been studied experimentally and by density functional theory (DFT) calculations. The standard oxidation enthalpy ΔH0Ox of oxygen deficient (Ca2CoO3)0.62(CoO2) was measured directly using simultaneous thermogravimetry and differential scanning calorimetry. ΔH0Ox was found to be in agreement with the prediction from a previously published defect chemical model based on purely thermogravimetrical analysis. A series of samples with different oxygen vacancy concentration was prepared by annealing in air, followed by rapid quenching. Room-temperature Raman spectroscopy showed a sharp mode at 700 cm–1 decreasing in intensity with increasing vacancy concentration. We discuss this observation as evidence for oxygen vacancies being preferably formed within the central layer of the Ca2CoO3 subsystem. DFT calculations demonstrated that the calculated electronic structure is sensitive to the chosen model of the crystal structure. Still, for all investigated models, the standard formation enthalpy of oxygen vacancies within the Ca2CoO3 moiety was much lower than that for a site within the CoO2 layer, in agreement with the presented experimental data. © 2014, American Chemical Society
In situ diffraction studies of iron ore sinter bonding phase formation: QPA considerations and pushing the limits of laboratory data collection
No full textThe formation and decomposition of silico-ferrite of calcium and aluminium (SFCA) and SFCA-I iron ore sinter bonding phases have been investigated using in situ synchrotron and laboratory X-ray diffraction (XRD) and neutron diffraction (ND). An external standard approach for determining absolute phase concentrations via Rietveld refinement-based quantitative phase analysis is discussed. The complementarity of in situ XRD and ND in characterising sinter phase formation and decomposition is also shown, with the volume diffraction afforded by the neutron technique reducing errors in the quantification of magnetite above ~1200 °C. Finally, by collecting 6 s laboratory XRD datasets and using a heating rate of 175 °C min−1, phase formation and decomposition have been monitored under heating rates more closely approximating those encountered in industrial iron ore sintering.© 2014 JCPDS-ICDD
3D Radiation Detectors: Charge Collection Characterisation and Applicability of Technology for Microdosimetry
No full textA study of charge collection in SINTEF 3D active edge silicon detectors was carried out at ANSTO using Ion Beam Induced Charge (IBIC) technique. An IBIC study has shown that several different geometries of 3D detectors have full depletion under low applied bias. The effect of fast neutron and gamma radiation on their charge collection efficiency was also investigated. A 3D active edge silicon detector technology has demonstrated extremely promising performance for application of the 3D Sensitive Volumes (SVs) fabrication methods to SOI microdosimetry.© 2014, IEEE
Magnetic transitions and the magnetocaloric effect in the Pr1−xYxMn2Ge2 system
No full textLayered rare earth compounds in the RMn2X2 series (R = rare-earth; X = Ge, Si) are of interest for potential cooling applications at lower temperatures as they enable the structural and magnetic behavior to be controlled via substitution of R, Mn, and X atoms on the 2a, 4d, and 4e sites respectively. We continue investigations of the Pr1−xYxMn2Ge2 magnetic phase diagram as functions of both composition and Mn–Mn spacing using X-ray and neutron diffraction, magnetization and differential scanning calorimetry measurements. Pr1−xYxMn2Ge2 exhibits an extended region of re-entrant ferromagnetism around x ∼ 0.5 with re-entrant ferromagnetism at inline image for Pr0.5Y0.5Mn2Ge2. The entropy values −ΔSM around the ferromagnetic transition temperatures inline image from the layered antiferromagnetic AFl structure to the canted ferromagnetic structure Fmc (typically inline image) have been derived for Pr1−xYxMn2Ge2 with x = 0.0, 0.2, and 0.5 for ΔB = 0–5 T. The changes in magnetic states due to Y substitution for Pr are discussed in terms of chemical pressure, external pressure, and electronic effects.© 2014, WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Single-Crystal Neutron Diffraction Study of Superstructure Ordering and Domain Behaviour in Brownmillerite-Type Ca2Fe2O5
No full textWe show that large single crystals of brownmillerite-type Ca2Fe2O5 can be grown using the floating-zone method under ambient pressure conditions, provided that the feed rods are pre-annealed to a very high density. Neutron diffraction data collected from these crystals show the emergence of a long-range ordered incommensurate phase at high temperature. The observation of this phase for the first time using neutrons proves that the incommensurate ordering of tetrahedral chains upon heating Ca2Fe2O5 is a truly long-range and bulk phenomenon. The results are used to compare and contrast the structures of Ca2Fe2O5 and Sr2Fe2O5, and are consistent with experimental observations of significantly higher oxide ionic conduction in the latter material
Identifying tsunami deposits in the absence of sand.
No full textTsunamis originating in South America are known to have affected Lyttelton Harbour, New Zealand, in the recent past. However, while there was clear evidence of inundation, in particular in 1960 and 2010, there was no report of any sand left behind. Our study aimed to search for evidence of these small historical tsunamis, in the absence of any visible sand layer. Shallow trenches revealed discontinuous layers of small grey mud clasts at various depths across the study area, most likely transported from the nearby harbour. The origin of these mud clast layers was investigated using sedimentological, geochemical and diatom analyses complemented by dating from 137Cs activity profiles and historical data. Subtle variations consistent with inclusions of marine mud such as a decrease in organic content and magnetic susceptibility and increases in geochemical markers (e.g. Ca, K, K/Rb, Si/Rb and Sr/Rb) were found in the sediment profile. Variations in diatom assemblages suggesting a marine influence were also recorded at similar depths, aligning with layers of mud clasts. Based on 137Cs activity profiles and historical data, these deposits were attributed to the 1960 Chile and 1964 Alaska tsunamis, and we also found evidence for an older deposit, possibly associated with the 1868 Arica tsunami. Sedimentary evidence for the 2010 Chile tsunami was not found at the study site, but our study revealed spatial variations in Ca, Cl and Sr concentrations that were inversely related to Ti concentrations. This was used to identify the landward extent of inundation by the 2010 event. We show that a broad multi-proxy analysis can distinguish even the subtle signatures of an inconspicuous deposit laid down by a small tsunami. © 2014,American Geophysical Union
Voxel modeling of rabbits for use in radiological dose rate calculations
No full textRadiation dose to biota is generally calculated using Monte Carlo simulations of whole body ellipsoids with homogeneously distributed radioactivity throughout. More complex anatomical phantoms, termed voxel phantoms, have been developed to test the validity of these simplistic geometric models. In most voxel models created to date, human tissue composition and density values have been used in lieu of biologically accurate values for non-human biota. This has raised questions regarding variable tissue composition and density effects on the fraction of radioactive emission energy absorbed within tissues (e.g. the absorbed fraction - AF), along with implications for age-dependent dose rates as organisms mature. The results of this study on rabbits indicates that the variation in composition between two mammalian tissue types (e.g. human vs rabbit bones) made little difference in self-AF (SAF) values (within 5% over most energy ranges). However, variable tissue density (e.g. bone vs liver) can significantly impact SAF values. An examination of differences across life-stages revealed increasing SAF with testis and ovary size of over an order of magnitude for photons and several factors for electrons, indicating the potential for increasing dose rates to these sensitive organs as animals mature. AFs for electron energies of 0.1, 0.2, 0.4, 0.5, 0.7, 1.0, 1.5, 2.0, and 4.0 MeV and photon energies of 0.01, 0.015, 0.02, 0.03, 0.05, 0.1, 0.2, 0.5, 1.0, 1.5, 2.0, and 4.0 MeV are provided for eleven rabbit tissues. The data presented in this study can be used to calculate accurate organ dose rates for rabbits and other small rodents; to aide in extending dose results among different mammal species; and to validate the use of ellipsoidal models for regulatory purposes. © 2015, Elsevier Ltd
Time-series of tritium, stable isotopes and chloride reveal short-term variations in groundwater contribution to a stream
No full textA major limitation to the assessment of catchment transit time (TT) stems from the use of stable isotopes or chloride as hydrological tracers, because these tracers are blind to older contributions. Yet, accurately capturing the TT
of the old water fraction is essential, as is the assessment of its temporal variations under non-stationary catchment dynamics.
In this study we used lumped convolution models to examine time series of tritium, stable isotopes and chloride in rainfall, streamwater and groundwater of a catchment
located in subtropical Australia. Our objectives were to determine the different contributions to streamflow and their
variations over time, and to understand the relationship between catchment TT and groundwater residence time. Stable
isotopes and chloride provided consistent estimates of TT in the upstream part of the catchment. A young component to streamflow was identified that was partitioned into quickflow (mean TT ≈ 2 weeks) and discharge from the fractured igneous
rocks forming the headwaters (mean TT ≈ 0.3 years).
The use of tritium was beneficial for determining an older contribution to streamflow in the downstream area. The best
fits between measured and modelled tritium activities were obtained for a mean TT of 16–25 years for this older groundwater
component. This was significantly lower than the residence time calculated for groundwater in the alluvial aquifer feeding the stream downstream (≈ 76–102 years), emphasising
the fact that water exiting the catchment and water stored in it had distinctive age distributions. When simulations were
run separately on each tritium streamwater sample, the TT of old water fraction varied substantially over time, with values
averaging 17 ± 6 years at low flow and 38 ± 15 years after
major recharge events. This counterintuitive result was interpreted as the flushing out of deeper, older waters shortly after
recharge by the resulting pressure wave propagation. Overall, this study shows the usefulness of collecting tritium data in
streamwater to document short-term variations in the older
component of the TT distribution. Our results also shed light on the complex relationships between stored water and water in transit, which are highly non-linear and remain poorly
understood. © Author(s) 2016. CC Attribution 3.0 License