A Survey of Electron Probe Microanalysis Using Soft Radiations: Difficulties and Presentation of a New Computer Program for Wavelength Dispersive Spectrometry

This paper aims to demonstrate that on-line peak integral technique with wavelength dispersive spectroscopy (WDS) provides accurate results with intensity measurement counting times as short as one or two minutes, owing to the high counting rates obtained with multilayer analyzers. A great advantage of a new computer program using this technique (available on SUN/UNIX work-stations operating Cameca SX-50 microprobes) consists in the original way that peak overlaps are treated. For each analytical point, overlapping counts emerging from an element B (B counts) are removed on-line from the measured raw counts in order to obtain the net counts corresponding to the element to be analyzed (element A). B counts are first measured on a proper standard containing B but not A. The effects of chemical bonding on the shape and the shift of peaks is clearly seen in the analysis of fluorine in topaz and lithium fluoride. Self-absorption effects, which usually distort the high energy side of L-series soft radiations, are generally inconsistent with the direct measurements of peak area fork-ratio determination. A method based on the conventional area/peak factor concept is proposed for this purpose

Spectral Decomposition of Wavelength Dispersive X-Ray Spectra: Implications for Quantitative Analysis in the Electron Probe Microanalyzer

The line shapes of Kα, Lα,β and Mα X-ray peaks of pure elements were analyzed by means of commercial wavelength dispersive spectrometers (WDS) attached to an electron probe micro-analyzer (EPMA). A pseudo-Voigt function, i.e., a linear combination of Gaussian and Lorentzian distributions, was used as a fitting profile for the X-ray peaks, with Gaussian offsets incorporated in the short wavelength (high energy) side to describe the observed asymmetry. The asymmetry of X-ray peaks resulting from both instrumental distortions and satellite bands may lead to discrepancies in quantitative analysis with the EPMA as a function of the procedure used for deriving X-ray intensities from WDS spectra, e.g., peak height, peak area, or peak decomposition. These effects have been illustrated by analyzing gold-copper metallic alloys and minerals containing gold at trace levels

Contributions of U-Th-Pb dating on the diagenesis and sediment sources of the Lower Group (BI) of the Mbuji-Mayi Supergroup (Democratic Republic of Congo)

In this paper, we present new age constraints for the lower part of the Meso-Neoproterozoic sedimentary Mbuji-Mayi Supergroup (Democratic Republic of Congo, DRC). This Supergroup preserves a large diversity of organic-walled microfossils, evidencing the diversification of early eukaryotes for the first time in Central Africa. We use different methods such as in situ U-Pb geochronology by LA-ICP-MS and U-Th-Pb chemical datings by Electron Microprobe on diagenetic and detrital minerals such as xenotimes, monazites and zircons. We attempt to better constrain the provenance of the Mbuji-Mayi sediments and the minimum age of the Mbuji-Mayi Supergroup to constrain the age of the microfossils. Results with LA-ICP-MS and EMP provide new ages between 1030 and 1065 Ma for the diagenesis of the lower part of the sedimentary sequence. These results are consistent with data on biostratigraphy supporting the occurrence of worldwide changes at the Mesoproterozoic/Neoproterozoic boundary

The effect of cation disorder on magnetic properties of new double perovskites La2NixCo1-xMnO6 (x = 0.2 - 0.8)

Solid solutions of new double perovskite oxides La2NixCo1-xMnO6 (x = 0.2, 0.25, 0.5, 0.75, 0.8) were synthesized by solid-state reaction method. The X-ray powder diffraction data show that all the compounds crystallize in the monoclinic structure with space group P21/n at room temperature. The elementary composition of the powders was determined by the electron Probe Microanalysis. Raman and IR spectra show strong bands at (520, 650 cm?1) and (426, 600 cm?1) respectively, attributed to the stretching vibration of Ni/Co-O and Mn-O bonds in the structure. The magnetic studies for all the compounds have been performed in both DC and AC magnetic fields in the temperature range from 2 to 300 K. All samples exhibit a main paramagnetic to ferromagnetic (PM-FM) transition between 232 K and 260 K, and their Curie temperature increases rapidly with increasing x values. Three samples with x = 0.2, 0.25 and 0.5 respectively display also a secondary PM-FM transition between 200 K and 208 K. The thermal variation of out of phase component of AC susceptibility presents also frequency-dependent transitions between 65 K and 110 K unfolding the existence of super-paramagnetic mono-domains in all samples. The band gap energy has been calculated and revealing semiconductor behavior for all samples

The reconstruction of the first copper-smelting processes in Europe during the 4th and the 3rd millennium BC: where does the oxygen come from?

International audienceFrom the end of Chalcolithic times (end of the 4th millennium BC) up to the end of the Bronze Age (1st millenium BC), copper production increases dramatically in Western Europe. However, due to the scarcity of technology-related archaeological data, the technological background sustaining the transition to mass production modes remains poorly understood. The main archaeological clues concerning metal production stem from the metallurgical waste, namely copper slags. Those complex materials may be a genuine chemical footprint of the process. In particular, it may bring new insights on one main issue of the process reconstruction: the origin of the oxygen in the system. A new analytical methodology based on both mass-balance calculation and quantification of Fe3+ contents in copper slags (Mössbauer spectroscopy, electronic microprobe and Synchrotron μ-XANES at the Fe-K-edge) has been set up. This methodology enables us to distinguish between the solid and gaseous sources of oxygen in a broad range of working conditions, thus yielding new features for the understanding of the first smelting processes dealing with copper sulphides in Western Europe 4000 years ago

Using the magnetic properties of Fe-serpentines for probing early alteration events in CM2 carbonaceous chondrites

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In situ identification and X-ray imaging of microorganisms distribution on the Tatahouine meteorite

Microorganisms were searched for among the complex microstructures observed on the surface of a fragment of the Tatahouine meteorite inherited from the Tunisian soil in which they were buried. In this view, the chemical compositions, particularly the nitrogen, phosphorus, and sulphur compositions, including the sulphur speciation, were investigated using scanning electron microscopy (SEM), electron probe microanalysis (EPMA) mapping, and scanning X-ray microscopy (SXM). A few 2-mum-thick filaments, partly covered by patches of calcite ensuring they were not deposited by a laboratory contamination, were observed by SEM. The EPMA maps show that the portions free of calcite of the filaments have low but constant contents of nitrogen, sulphur, and phosphorus. The SXM maps were recorded at 2473.5, 2478 and 2482.2eV, which are respectively characteristic for amino acid-linked sulphur, sulphite (SO32-), and sulphate (SO42-). The portions of the filaments detected by EPMA are also those that are enriched in amino acid linked sulphur. The calculated (N/S) elemental ratio is consistent with the one of the dehydrated Escherichia coli matter, contrary to the much lower (P/S) elemental ratio. In living cells, the bulk N and S elements are mainly located in large polymers by covalent bonds, whereas a significant amount of P belongs to small and reactive molecules. We thus can propose that the observed microstructures are dehydrated micro organisms, in which most of the elements that were composing the polymers were retained, whereas the small electrolytes and molecules were removed. (C) 2004 Elsevier B.V. All rights reserved