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Abstract: Energy scale calibration and reliable intensity measurement are the main issues related to the collection of good spectroscopy data. The accurate determination of the energy scale is often established by using foils of optimum thickness to calibrate the monochromator. However, mechanical issues with the monochromator, movement of the source, or even the resolution of the spectrometer can have an effect on the measured energy scale. For the issue of accurate intensity measurements, calibrated detectors are necessary to ensure a reliable measurement of the spectroscopic signal, both in transmission and fluorescence detection modes. In this paper a review of the most common techniques used for energy calibration and for collecting X-ray absorption spectroscopy data is given, together with a brief description of the factors that have an impact on the intensity of the measured signal. A brief description of the versatile X-ray absorption spectroscopy beamline, I20, at Diamond Light Source is also presented, giving particular emphasis on how the beamline design has been undertaken to tackle these key issues. In particular, the use of a four-bounce monochromator will be discussed, highlighting the advantages of the device for the measurement of spectroscopy data.

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Abstract: Although at 1 atm pressure the oxidation state of W in silicate melts is 6 + at oxygen fugacities from air down to several logfO2 units below Fe-FeO (IW) equilibrium, Cottrell et al. (2009) suggested that, at pressures above 6 GPa, W becomes predominantly 4 + in this oxygen fugacity range. Wade and Wood (2005), using a similar, but expanded metal-silicate partitioning dataset found, however, no evidence for an oxidation state change. In order to resolve the issue we collected tungsten L3 edge XANES spectra of a series of synthetic tungsten- bearing glass standards and of silicates from a range of high-pressure (1.5 to 25 GPa) metal/silicate partitioning experiments. Glass standards were made at 1 atm pressure and equilibrated at oxygen fugacities spanning a range from approximately 5.5 log units below the Fe-FeO buffer (IW-5.5) to Air. Metal-silicate partitioning experiments were performed at oxygen fugacities between IW-6.2 and IW-1 and at pressures between 1.5 and 25 GPa. At low pressures and oxygen fugacities above IW-3.5, W exists in the silicate melt almost exclusively as W6 + (identical L3-edge energy to WO3) with the progressive reduction to W4 + completed by about IW-6. The XANES spectra of W from experiments at 6, 7 and 25 GPa are completely consistent with those from 1 atm and 1.5 GPa experiments and with that of WO3. We conclude that there is no change of oxidation state with increasing pressure to 25 GPa and that modelling of the oxygen-fugacity dependence of core formation requires use of a + 6 oxidation state of W.

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Abstract: Melt quenched silicate glasses containing calcium, phosphorus and alkali metals have the ability to promote bone regeneration and to fuse to living bone. Of these glasses 45S5 Bioglasss is the most widely used being sold in over 35 countries as a bone graft product for medical and dental applications; particulate 45S5 is also incorporated into toothpastes to help remineralize the surface of teeth. Recently it has been suggested that adding titanium dioxide can increase the bioactivity of these materials. This work investigates the structural consequences of incorporating 4 mol% TiO2 into Bioglasss using isotopic substitution (of the Ti) applied to neutron di\ufb00raction and X-ray Absorption Near Edge Structure (XANES).

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Abstract: Zircon (ZrSiO4) is a durable mineral found in most igneous rocks; it is highly retentive of the trace element concentrations it acquires at crystallisation, and its high initial concentrations of U and Th relative to Pb make it the most important mineral for radiometric dating. Therefore, it is a valuable archive of magmatic processes, particularly with regard to those occurring on the early Earth. Based on crystal chemistry, anomalous Ce and Eu concentrations in zircon relative to other rare earth elements (REE) seem likely to reflect the oxidation state of the magma. Zircons were grown experimentally under controlled conditions of oxygen fugacity (fO2) and the crystals and coexisting glass were analysed by SIMS and LA-ICP-MS to examine the covariation of the partition coefficients of Ce and Eu, as well as those of other trace elements. This revealed that with increasing fO2, Ce becomes more compatible and Eu and U become less compatible. There is a narrow window of fO2s in which a Ce and a Eu anomaly coexist. Literature data allow the partitioning data obtained for the heavy REE in this study to be extrapolated to other temperatures. To allow extrapolation of the partitioning experiments, Ce- and Eu-doped glasses of various melt compositions were prepared at a range of fO2s and temperatures. X-ray absorption near edge structure (XANES) spectroscopy of these glasses was carried out at the LIII-edge of these elements to determine their oxidation state ratios. Because of beam damage effects for the Eu-bearing glasses, a limited number of XANES spectra were recorded in situ at 1400 °C, and some samples were analysed by electron paramagnetic resonance spectroscopy. The results obtained were compared to trace element concentrations in zircons from some natural samples, and suggestions for future work made.