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Abstract: We present further analyses of a previous experiment published in 2016 where the distribution, concentration and correlation of iron, zinc, copper and sulphur in the choroid of the eye in young and aged old world primates (Macaca fascicularis) was studied with synchrotron X-ray fluorescence with a 2 μm resolution. The results indicate that iron accumulates in hotspots in the choroid with age with fluorescence intensity ranging from 2- to 7-fold (1002–3752 ppm) the mean level in the choroidal stroma (500 ppm) and maximum iron levels in blood vessel lumina. Iron hotspots with iron ppm > 1000 preferentially contained Fe3+ as demonstrated by Perls staining. There was a strong spatial co-localisation and correlation between copper and zinc (Pearson’s correlation coefficient 0.97), and both elements with sulphur in the choroid of young animals. However, these are reduced in the choroid of aged animals and lost in the iron hotspots. The lack of proportional co-distribution suggests that iron accumulation does not induce a concomitant increase in zinc, copper or zinc-, copper-metalloproteins. It is possible that the iron hotspots are ferritin or hemosiderin molecules loaded with Fe3+ in stable, insoluble, non-toxic complexes without a significant oxidative environment.

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Abstract: This manuscript presents the current status and technical details of the Spectroscopy Village at Diamond Light Source. The Village is formed of four beamlines: I18, B18, I20-Scanning and I20-EDE. The village provides the UK community with local access to a hard X-ray microprobe, a quick-scanning multi-purpose XAS beamline, a high-intensity beamline for X-ray absorption spectroscopy of dilute samples and X-ray emission spectroscopy, and an energy-dispersive extended X-ray absorption fine-structure beamline. The optics of B18, I20-scanning and I20-EDE are detailed; moreover, recent developments on the four beamlines, including new detector hardware and changes in acquisition software, are described.

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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.

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Abstract: We have constructed a Time-Resolved X-ray Excited Optical Luminescence (TR-XEOL) detection system at the Microfocus Spectroscopy beamline I18 at the Diamond Light Source. Using the synchrotron in "hybrid bunch mode", the data collection is triggered by the RF clock, and we are able to record XEOL photons with a time resolution of 6.1 ps during the 230 ns gap between the hybrid bunch and the main train of electron bunches. We can detect photons over the range 180-850 nm using a bespoke optical fibre, with X-ray excitation energies between 2 and 20 keV. We have used the system to study a range of feldspars. The detector is portable and has also been used on beamline B18 to collect Optically Determined X-ray Absorption Spectroscopy (OD-XAS) in QEXAFS mode.

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Abstract: Young igneous rocks from a range of tectonic settings exhibit various Uranium-series (Useries) disequilibria. The U-series systematics of Mid-ocean-ridge basalts (MORBs) have been attributed to mantle melting, while those of arc basalts are widely thought to be slabfluid signatures. Mid-ocean-ridge and arc U-series models generally assume that U4+ is the only oxidation state relevant to mantle melting processes, however the potential for the stabilisation of U5+ and/or U6+ has recently been proposed for some arc lavas. To determine the oxidation state of U in geological melts, and to assess the relative stabilities of U4+, U5+, and U6+ under mantle conditions, X-ray absorption near edge structure (XANES) spectra were recorded from synthetic analogues, including an Fe-bearing MORB composition. Spectra were collected from quenched glasses equilibrated at 1400 °C and oxygen fugacities (fO2s) between logfO2 = -18 and +4.7 (QFM-11.7 to QFM+11), and from equivalent high temperature melts using a custom designed XAS furnace. Spectra were collected at both the U L3- and M4-edges, as the variation of the M4-edge spectral line-shape could be unambiguously linked to oxidation state changes in the glasses, while the higher energy of the L3-edge was better suited to in situ studies. The variation of the XANES spectra as a function of fO2 allowed U5+ to be identified as a major component in both the MORB glasses and their original melts, and a methodology was developed to accurately quantify their U oxidation state proportions. The proportion of U4+ was found to be highly sensitive to fO2 at conditions relevant to mantle melting, with U5+/ΣU varying between ~0.1 and 0.5 between QFM-1 and QFM+2 and pressures equivalent to mantle depths of ≥ 15 km. U-series models assuming melting of a variably oxidised mantle wedge can produce a wide range of U-series signatures that are consistent with many arc basalts. In contrast, the stability of even small proportions of U5+ in the melt may present a problem for those models currently attributing the 230Th excesses of MORBs to mantle melting in the spinel lherzolite field.