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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: We present Ba L3-X-ray Absorption Fine Structure (XAFS) data from a suite of barium carbonates (witherite, alstonite, barytocalcite), hydroxides, sulfate(vi) (barite) and a Ba-bearing organic compound to explore whether Ba L3-XAFS could be used to fingerprint structural states in biominerals such as celestite, aragonite and calcite. Although there is a general similarity between all X-ray Absorption Near Edge Structure (XANES), subtle differences are observed in detail, which allow almost all phases to be distinguished. The XANES are considered as composites of four components, termed ‘A’ (5255 eV), ‘B’ (5258 eV), ‘C’ (5268 eV) and ‘D’ (5273 eV). ‘A’ is observed in barium hydroxides and most visible in the first derivatives of the XANES data. The minimum after the Ba L3 white line lies at 5257 eV for most materials but higher (5261 eV) for barium hydroxides due to the influence of the ‘A’ component. ‘B’ is present in aragonite-group minerals (witherite and alstonite) and may be a fingerprint of that structural state. ‘C’ and ‘D’ overlap and form a board hump at ∼ 5270 eV, but the relative proportions of ‘C’ and ‘D’ are variable between phases and are to some degree diagnostic. Refinement of Extended X-ray Absorption Fine Structure (EXAFS) allows estimates of first shell (Ba–O) bond distances in all materials, which are within 4% of average distances estimated from diffraction studies. Subsequent shells (Ba–S for barite; Ba–metal in witherite, alstonite and barytocalcite) can be resolved. The state of Ba:Ca order in alstonite and barytocalcite is successfully modelled and both are found to be fully ordered. The significant static disorder in Ba-bearing minerals is accommodated successfully by large Debye–Waller values in the refinements. Combinations of XANES and EXAFS allow all phases to be identified, with the exception that the two hydrated barium hydroxides cannot be distinguished from each other. The XANES of a celestite (SrSO4 containing ∼ 100 ppm Ba) is comparable to the barite spectra after only seven cycles (collected over < 5 h), showing that XANES can be resolved in samples with low Ba concentrations. However we were unable to analyse successfully an aragonitic Porites coral skeleton (containing ∼ 3–4 ppm Ba) using the current instrumentation due to the proximity in energy of Ca Kα secondary X-radiation to the Ba Lα energy and which overloaded the X-ray detector. The use of multilayer crystal detectors will be required to resolve the Ba Lα energy in calcium carbonate samples containing low Ba concentrations. Alternatively Ba EXAFS may be accessible through the Ba K edge.

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Abstract: Uraniferous particles from contaminated environmental samples were analysed by scanning electron microscopy with energy dispersive X-ray analysis (SEM-EDXA) and microfocus extended X-ray absorption fine structure (μEXAFS) spectroscopy. The particles of interest are uranium oxides, which were released into the environment by the combustion of scrap depleted uranium (DU) metal at a factory in Colonie, New York, USA. Most of the identified particles appear to have primary, `as emitted' morphologies; some have evidence of minor dissolution, including corrosion pitting. Polycrystalline and often hollow microscopic spheres were identified, which are similar to particles produced by DU munitions impacting armoured targets. They are attributed to the autothermic oxidation of melt droplets. The compositions of the analysed spheres are dominated by UO2+x with variable amounts of U3O8, two of the least soluble and least bioaccessible phases of U. These particles, collected from dusts and soils, have survived more than 25 y in the terrestrial environment. This study further supports the case for using Colonie as an analogue for battlefield DU contamination.

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Abstract: Third generation synchrotrons allowed to perform experiments which had a major impact in the field of environmental science and related disciplines such as mineralogy and cultural heritage. This paper presents some basic concepts on synchrotron radiation and the fundamentals of X-ray absorption fine spectroscopy - XAFS - are introduced and accompaigned with three examples on cultural heritage and mineralogy with the aim to show the opportunities those XAFS techniques provide. The first example is the study lustre ceramics found in an archaeological site in Paterna to elucidate how they were produced, the second example is related to the systematic study of vermillion pigments from across Europe and Asia to target possible useful trace elements involved in their decay, and finally a third example is shown related to the study of a mineralogical problem aiming to understand the speciation and association of Ni in a laterite from Moa Bay (Cuba) where the sorption of Ni on Mn oxyhydroxides is taking place.