For X-ray tubes in lab based computed micro-tomography systems, off-focal X rays are those emitted from the source but not produced at the primary focal spot of the electron beam. They can be attributed to both electron and photon scatter within the X-ray tube. Off-focal X rays can represent a significant fraction of the total X-ray flux and lead to artefacts in the radiographs, and reconstructed tomographic volumes, degrading contrast and resolution. Therefore, they are an undesirable feature in industrial and medical X-ray CT scanners. In this work, a general model of an X-ray tube with a transmission target has been developed in TOPAS, a Monte Carlo (MC) simulation extension to GEANT4. MC simulations enable: (1) the analysis of the origin of various types of off-focal X rays; (2) quantification of the prevalence of each type for a specific tube geometry and (3) replication and understanding of experimental results affected by off-focal X rays. Our MC analysis herein shows that the amount of off-focal X rays can represent up to 25% of total X-ray flux. The most prevalent off-focal X rays were found to be the X rays created by the electrons back-scattered from the target into the aperture and generating X rays.

3D-visualisation of a Bentheimer sandstone sample (2 × 2 × 8.3 mm3) using Paraview: 1. The high-resolution micro-CT data (1.66 μm voxel size, acquired: Australian National University, CTLab [1, 2, 3]), 2. Two phase segmentation (black and yellow represents void and grain, respectively), 3. Network model of the connected macropores (generated with OPENPNM), 4. Disconnected microporosity defined as isolated voids smaller than 3.15 × 10–6 mm3.

A better understanding of ore breakage and fragmentation is a key to meeting important industrial challenges as the mining industry is exploring and extracting more low-grade ore deposits [1].

Off-focal x rays are an undesirable feature in industrial and medical x-ray computed-tomography scanners that contributes the effects of a large defocused source. They lead to artefacts in tomographic volumes that degrade contrast and resolution. A simple model of an x-ray tube with a transmission target has been developed in Topas, a Monte Carlo (MC) simulation extension to Geant4, to improve the understanding of the origin of off-focal x rays. From the analysis of the MC simulations we are able to identify the origin of various types of off-focal x rays and characterise their spatial distribution and energy spectra. We can then propose and test different mitigation methods, based both on hardware additions as well as improvements in the image reconstruction or data postprocessing.

At CTLab we have recently commissioned a 300keV x-ray tomography system capable of imaging metallic parts and rock cores with diameters over 100mm. This new imaging regime manifests artefacts in the reconstructed tomographic volumes that resemble those from incoherent x-ray scatter from the object. However, through the experimental investigation outlined herein, we have determined these artefacts to be primarily due to off-focal, or secondary, x rays emitted from the x-ray source. All micro-focus x-ray sources tested, (both transmission and reflection targets), exhibited off-focal x rays to a greater or lesser extent (6 different x-ray source models from 4 different manufacturers). We also demonstrate that off-focal x rays may have received limited attention to date since the artefacts they cause are only severe for highly attenuating samples. Here our aim is to fully understand and characterise this phenomenon in order to incorporate it into the imaging model and mitigate the associated artefacts in computed tomography.

A better understanding of the relation between ore fragmentation and ore texture is a key to the energy efficient extraction of targeted minerals from low grade ore deposits. In this study, X-ray micro-computed tomography is employed to study mineral liberation during the tensile failure and onset of fragmentation of a copper ore. We present the results of experiments based on a high-pressure instrument enabling micro-mechanical studies to be carried out in-situ (inside a micro-CT scanner). This experimental platform enables mapping in 3D of the evolution of a sample of copper ore during an in-situ fragmentation test. The fragmentation occurs quasi-statically via tensile-activated nucleation and growth of multiple cracks producing a complex fracture network. Coupling breakage with microstructural information, we determine quantitatively the impact of ore textural features on fracture patterns and mineral liberation. This information can be compared to the ore mechanical behaviour, in particular to measurements of the deformation energy, the strain deformation field or the stress relaxation response. The copper liberation, fragment size distribution and breakage patterns are statistically characterised and related to two dominant comminution mechanisms which are clearly identified in the sequence of tomographic images. Our results show that in-situ micro-CT experiments could inform new studies of ore fragmentation at the laboratory scale and may offer new avenues to address current challenges in the design of efficient comminution processes.

Calcifying organisms and their exoskeletons support some of the most diverse and economically important ecosystems in our oceans. Under a changing climate, we are beginning to see alterations to the structure and properties of these exoskeletons due to ocean acidification, warming and accelerated rates of bioerosion. Our understanding has grown as a result of using micro‐computed tomography (µCT) but its applications in marine biology have not taken full advantage of the technological development in this methodology. We present a significant advancement in the use of this method to studying decalcification in a marine calcifier. We present a detailed workflow on best practice for µCT image processing and analysis of marine calcifiers, designed using coral skeletons subjected to acute, short‐term microbial bioerosion. This includes estimating subresolution microporosity and describing pore space morphological characteristics of macroporosity, in perforate and imperforate exoskeletons. These metrics are compared between control and bieroded samples, and are correlated with skeletal hardness as measured by nanoindentation. Our results suggest that using subresolution microporosity analysis improves the spatiotemporal resolution of µCT data and can detect changes not seen in macroporosity, in both perforate and imperforate skeletons. In imperforate samples, the mean size and relative number of pores in the macroporous portion of the images changed significantly where total macroporosity did not. The increased number of pores and higher microporosity are both directly related to a physical weakening of the calcareous exoskeletons of imperforate corals only. In perforate corals, increased macroporosity was accompanied by an overall widening of pore spaces though this did not correlate with sample hardness. These novel techniques complement traditional approaches and in combination demonstrate the potential for using µCT scanning to sensitively track the process of decalcification from a structural and morphological perspective. Importantly, these approaches do not necessarily rely on ultra‐high resolution (i.e. single micron) scans and so maintain the accessibility of this technology. The continued optimization of these tools for a variety of marine calcifiers will advance our understanding of the effect of climate change on marine biogenic calcified structures.

Archaeological parenchyma is analysed using microCT to enable virtual histological examination and taxonomic identification to species level. MicroCT images are compared with reflected light microscopy (RLM) and scanning electron microscopy (SEM) images of fresh, desiccated and charred reference specimens. These results reveal differences in cell dimensions depending upon sample preparation and highlight the importance of using appropriately prepared reference material. A reference library is provided as supplemental material to address a lack of available imagery of reference specimens. MicroCT analysis confirms previous, more tentative, identifications of fragments of archaeological parenchyma from relatively recent archaeological contexts at Kuk Swamp, highlands of Papua New Guinea. Five archaeobotanical fragments are described in detail and with varying levels of confidence to sugarcane (Saccharum officinarum) and sweet potato (Ipomoea batatas). The study demonstrates the potential of non-destructive microCT for the identification of archaeological parenchyma.

Severe marine heatwaves have recently become a common feature of global ocean conditions due to a rapidly changing climate [1, 2]. These increasingly severe thermal conditions are causing an unprecedented increase in the frequency and severity of mortality events in marine ecosystems, including on coral reefs [3]. The degradation of coral reefs will result in the collapse of ecosystem services that sustain over half a billion people globally [4, 5]. Here, we show that marine heatwave events on coral reefs are biologically distinct to how coral bleaching has been understood to date, in that heatwave conditions result in an immediate heat-induced mortality of the coral colony, rapid coral skeletal dissolution, and the loss of the three-dimensional reef structure. During heatwave-induced mortality, the coral skeletons exposed by tissue loss are, within days, encased by a complex biofilm of phototrophic microbes, whose metabolic activity accelerates calcium carbonate dissolution to rates exceeding accretion by healthy corals and far greater than has been documented on reefs under normal seawater conditions. This dissolution reduces the skeletal density and hardness and increases porosity. These results demonstrate that severe-heatwave-induced mortality events should be considered as a distinct biological phenomenon from bleaching events on coral reefs. We also suggest that such heatwave mortality events, and rapid reef decay, will become more frequent as the intensity of marine heatwaves increases and provides further compelling evidence for the need to mitigate climate change and instigate actions to reduce marine heatwaves.

The aim of this paper is to develop a novel specimen configuration optimised for developing and validating structure-property relationships for textile carbon fibre reinforced polymers (CFRPs). The specimen is designed to be imaged non-destructively using X-ray Microtomography (μCT), but is also optimised for in- and ex-situ mechanical testing. The investigation bridges a gap in current research where modified/enhanced (i.e. contaminated) CFRPs are often used to obtain suitable reconstructions to analyse. This paper looks at identifying the textile architecture of composites at the meso-level without the use of contrast enhancement agents (i.e. uncontaminated) and then proposes the optimum specimen size and scanning parameters to achieve successful reconstructions of the materials system. It was found that the Histogram of Oriented Gradients (HOG) gave the best segmentation outcome when the specimen was sized to fit at least two voxels within a fibre width. In addition to this prepping the specimen to include a cast epoxy jacket prevented CT artefacts during reconstruction. The application of these results will assist researchers in better understanding the evolution of microcracks and damage in textile composites while enabling physics based multiscale modelling approaches to be validated with realistic textile architectures.

We study quasi-static drainage displacement experiments in Bentheimer sandstone micro-cores using X-ray computed microtomography. Two nonwetting fluids, air and n-decane, are investigated, under high and low flow rate conditions. Experimental conditions consider viscosity ratios that vary by a factor of 40, and capillary numbers that range five orders of magnitude; but all experiments investigated are conducted under nominally capillary-dominated conditions, indicating that drainage displacements should demonstrate percolation-like invasion patterns. However, we observe significant and prevalent snap-offof nonwetting phase under all experimental conditions, a phenomena not predicted by the conceptual model of percolation invasion. We further observe that the size and persistence of snapped-offganglia are influenced by the experimental flow rate and the nonwetting phase fluid. The quasi-static experimental observations are supported by lattice-Boltzmann modelling of drainage dynamics. These findings indicate that current conceptual models of drainage are incomplete, with implications for future experimental and modelling studies as well as engineering applications.

Research Article| November 01, 2018 Unravelling the Consequences of SO2–Basalt Reactions for Geochemical Fractionation and Mineral Formation Andrew B. Palm; Andrew B. Palm Research School of Earth Sciences, Australian National University, Canberra ACT 2601, Australia Search for other works by this author on: GSW Google Scholar Penelope L. King; Penelope L. King Research School of Earth Sciences, Australian National University, Canberra ACT 2601, Australia Search for other works by this author on: GSW Google Scholar Christian J. Renggli; Christian J. Renggli Research School of Earth Sciences, Australian National University, Canberra ACT 2601, Australia Search for other works by this author on: GSW Google Scholar Richard L. Hervig; Richard L. Hervig School of Earth and Space Exploration, Arizona State University, Tempe AZ 85287, USA Search for other works by this author on: GSW Google Scholar Kim N. Dalby; Kim N. Dalby Department of Chemistry, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen, Denmark Search for other works by this author on: GSW Google Scholar Anna Herring; Anna Herring Research School of Physics and Engineering, Australian National University, Canberra ACT 260, Australia Search for other works by this author on: GSW Google Scholar Terrence P. Mernagh; Terrence P. Mernagh Research School of Earth Sciences, Australian National University, Canberra ACT 2601, Australia Search for other works by this author on: GSW Google Scholar Stephen M. Eggins; Stephen M. Eggins Research School of Earth Sciences, Australian National University, Canberra ACT 2601, Australia Search for other works by this author on: GSW Google Scholar Ulrike Troitzsch; Ulrike Troitzsch Research School of Earth Sciences, Australian National University, Canberra ACT 2601, Australia Search for other works by this author on: GSW Google Scholar Levi Beeching; Levi Beeching Research School of Physics and Engineering, Australian National University, Canberra ACT 260, Australia Search for other works by this author on: GSW Google Scholar Leslie Kinsley; Leslie Kinsley Research School of Earth Sciences, Australian National University, Canberra ACT 2601, Australia Search for other works by this author on: GSW Google Scholar Paul Guagliardo Paul Guagliardo Centre for Microscopy, Characterization and Analysis, University of Western Australia, M010 Perth WA 6009, Australia Search for other works by this author on: GSW Google Scholar Reviews in Mineralogy and Geochemistry (2018) 84 (1): 257–283. https://doi.org/10.2138/rmg.2018.84.7 Article history first online: 09 Nov 2018 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Andrew B. Palm, Penelope L. King, Christian J. Renggli, Richard L. Hervig, Kim N. Dalby, Anna Herring, Terrence P. Mernagh, Stephen M. Eggins, Ulrike Troitzsch, Levi Beeching, Leslie Kinsley, Paul Guagliardo; Unravelling the Consequences of SO2–Basalt Reactions for Geochemical Fractionation and Mineral Formation. Reviews in Mineralogy and Geochemistry 2018;; 84 (1): 257–283. doi: https://doi.org/10.2138/rmg.2018.84.7 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyReviews in Mineralogy and Geochemistry Search Advanced Search Major and trace elements in igneous and metamorphic rocks are commonly used to infer their petrogenesis (e.g., Carmichael et al. 1974; Wilson 1989; Pearce and Parkinson 1993). To date, our understanding of element transport is informed by diffusion data (e.g., Zhang 2010; Spandler and O’Neill 2010) and partitioning measurements that quantify the fractionation of an element between a mineral and a melt, aqueous fluid or metal phase (e.g., Beattie et al. 1993; Pearce and Parkinson 1993; Schott et al. 2009; Rollinson 2014). However, there is a dearth of data on the... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Near-field x-ray refraction (phase) contrast is unavoidable in many lab-based micro-CT imaging systems. Quantitative analysis of x-ray refraction (a.k.a. phase retrieval) is in general an under-constrained problem. Regularizing assumptions may not hold true for interesting samples; popular single-material methods are inappropriate for heterogeneous samples, leading to undesired blurring and/or over-sharpening. In this paper, we constrain and solve the phase-retrieval problem for heterogeneous objects, using the Alvarez-Macovski model for x-ray attenuation. Under this assumption we neglect Rayleigh scattering and pair production, considering only Compton scattering and the photoelectric effect. We formulate and test the resulting method to extract the material properties of density and atomic number from single-distance, dual-energy imaging of both strongly and weakly attenuating multi-material objects with polychromatic x-ray spectra. Simulation and experimental data are used to compare our proposed method with the Paganin single-material phase-retrieval algorithm, and an innovative interpretation of the data-constrained modeling phase-retrieval technique.

Rice (Oryza sativa) was domesticated in the Yangtze Valley region at least 6000-8000 years ago, yet the timing of dispersal of domesticated rice to Southeast Asia is contentious. Often rice is not well-preserved in archaeobotanical assemblages at early Neolithic sites in the wet tropics of Southeast Asia and consequently rice impressions in pottery have been used as a proxy for rice cultivation despite their uncertain taxonomic and domestication status. In this research, we use microCT technology to determine the 3D microscale morphology of rice husk and spikelet base inclusions within pottery sherds from early Neolithic sites in Vietnam. In contrast to surface impressions, microCT provides images of the entire husk and spikelet base preserved within the pottery, including the abscission scar characteristic of domesticated rice. This research demonstrates the potential of microCT to be a new, non-destructive method for the identification of domesticated plant remains within pottery sherds, especially in contexts where archaeobotanical preservation is poor and chaff-tempered sherds are rare and unavailable for destructive analysis. The method has the potential to greatly advance the understanding of crop domestication and agricultural dispersal for ceramic cultures in different parts of the world.

In the context of large-angle cone-beam tomography (CBCT), we present a practical iterative reconstruction (IR) scheme designed for rapid convergence as required for large datasets. The robustness of the reconstruction is provided by the "space-filling" source trajectory along which the experimental data is collected. The speed of convergence is achieved by leveraging the highly isotropic nature of this trajectory to design an approximate deconvolution filter that serves as a pre-conditioner in a multi-grid scheme. We demonstrate this IR scheme for CBCT and compare convergence to that of more traditional techniques.

Extended abstract of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – August 8, 2013.

Atomic oxygen has been studied using angle resolved photoelectron spectroscopy (PES) and constant-ionic-state (CIS) measurements using radiation from the Elettra synchrotron as the photon source. Relative partial photoionization cross-sections and angular distributions for the O+(4S) ← O(3P) and O+(2D) ← O(3P) ionizations have been measured as a function of photon energy from threshold (13.6 eV) to 19.0 eV. Comparison of the results obtained with recent experimental work performed at lower resolution reveals a number of differences and comparison with results of recent calculations shows the need for the inclusion of coupling intermediate between the j-j and L-S limits in future calculations of photoionization cross-sections and angular distributions. This work has demonstrated the feasibility of and results to be expected from angle resolved PES and CIS measurements on reactive intermediates at Elettra, a third-generation synchrotron source, and further studies on small molecular radicals are proposed.

The thermal decompositions of 2-azidoethanol and 2-azidoethyl acetate have been studied by matrix isolation infrared spectroscopy and real-time ultraviolet photoelectron spectroscopy. The products that were detected in a flow system at different temperatures (CH2NH, H2CO, N-2, CO, and HCN from N3CH2CH2OH and C2H4, CH2NH, HCN, CO2, and N-2 from N3CH2COOCH2CH3) allowed mechanisms for decomposition to be proposed. The experimental evidence obtained is consistent with 2-azidoethyl actetate decomposing via a concerted mechanism, similar to that found previously for azidoacetic acid, whereas the 2-azidoethanol decomposition is consistent with a stepwise decomposition mechanism as observed previously for azidoacetone.