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Abstract: Sulfur is a key volatile element in magmatic systems that exists in many phases (e.g. melt or gas), in multiple-oxidation states (S²⁻, S⁴⁺ and S⁶⁺), and has more than one stable isotope (e.g. ³²S and ³⁴S). Therefore, by measuring S, information regarding the conditions of a magma can be acquired. The aim of this work is to investigate what S can tell us about the behaviour of late-stage lunar basaltic magmas. An analytical protocol was developed to simultaneously measure S and Cl abundances and isotopes of lunar apatite in eleven lunar basalts with nano-scale secondary ion mass spectrometry (NanoSIMS). Additionally, a method was developed to measure the oxidation state of S in apatites of five mare basalts with X-ray absorption near-edge structure (XANES) spectroscopy at the S K-edge, making it possible to compare S oxidation state and S isotopes of lunar apatite for the first time. Lunar apatites contain ~20–2,800 ppm S, with δ³⁴S values between -33.3 ± 3.8‰ and +36.4 ± 3.2‰ (2σ). The Cl abundance is ~350–7,230 ppm, with δ³⁷Cl values of +6.5‰ ± 0.9‰ to +36.5‰ ± 1.1‰ (2σ). All of the apatites have S⁶⁺/ΣS(tot) ratios of >0, with average S⁶⁺/ΣS(tot) values between 0.05 and 0.55. An absence of correlation between S and Cl isotopes suggests a lack of evolutionary relationship between S and KREEP-rich components. The direction of S isotope fractionation, negative or positive, can be explained by degassing of H₂S and SO₂ from a relatively reduced (S²⁻) or oxidized (SO₄²⁻) late-stage silicate melt, respectively. The historical existence of relatively oxidized late-stage silicate melts is also evidenced by the presence of S⁶⁺ in lunar apatite. A positive trend is apparent between S⁶⁺/ΣS(tot) and δ³⁴S which is indicative of the dependence of S isotope fractionation on the oxygen fugacity of the late-stage silicate melt.

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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.