J. Trincavelli

Model for the bremsstrahlung spectrum in EPMA. Application to standardless quantification

The Kramers expression was modi‐ed after ‐tting 52 spectra from targets of diverse composition at several incident energies. The function obtained describes adequately the continuum x-ray spectrum observed when a bulk, homogeneous and polished sample is irradiated by an electron beam with energies ranging from 5 to 35 keV. The targets considered are pure and multicomponent, covering elements from boron to bismuth. In addition to simplicity, the new expression shows very good agreement with measured spectraEmuch closer than other models assessed. The proposed function was applied to a standardless quanti‐cation method based on peak-to-background ratios. 1998 John Wiley & Sons, Ltd.

Comparison of Φ (ρz) Curve Models in EPMA

Several authors have proposed different models for the ionization distribution function Φ(ρz). This paper presents a comparison of three of the most successful models for Φ(ρz): Packwood and Brown’s Gaussian model including Bastin et al.’s and Riveros et al.’s versions, the quadrilateral model proposed by Sewell et al. and Pouchou and Pichoir’s model. In general, all the tested models showed similar performances. Finally the advantages of the models related to basic principles over the mathematically optimized ones are considered.

L-shell radiative transition rates by selective synchrotron ionization

Relative L-shell radiative transition rates were obtained for a number of decays in Gd, Dy, Er, Yb, Hf, Ta and Re by means of a method for refining atomic and experimental parameters involved in the spectral analysis of x-ray irradiated samples. For this purpose, pure samples were bombarded with monochromatic synchrotron radiation tuning the incident x-ray energy in order to allow selective ionization of the different atomic shells. The results presented are compared to experimental and theoretical values published by other authors. A good general agreement was found and some particular discrepancies are discussed.

Analytical expression for K- and L-shell cross sections of neutral atoms near ionization threshold by electron impact

An analytical expression is proposed to describe the K- and L-shell ionization cross sections of neutral atoms by electron impact over a wide range of atomic numbers (4 ≤ Z ≤ 79) and over voltages U < 10. This study is based on the analysis of a calculated ionization cross section database using the distorted-wave first-order Born approximation (DWBA). The expression proposed for cross sections relative to their maximum height involves only two parameters for each atomic shell, with no dependence on the atomic number. On the other hand, it is verified that these parameters exhibit a monotonic behaviour with the atomic number for the absolute ionization cross sections, which allows us to obtain analytical expressions for the latter.

MULTI: an interactive program for quantitation in EPMA

A versatile interactive program for quantifying bulk samples and particles in electron probe microanalysis is presented. The program was developed with the purpose of allowing the analyst to choose among different matrix-correction models and several expressions for the parameters involved. It was written in Pascal and runs on any IBM compatible personal computer with no special requirements. The program was tested on a number of geological and synthetic samples of known compositions. Special applications which show the usefulness of the program are described. Copyright

Effects of the carbon coating and the surface oxide layer in electron probe microanalysis.

Effects related with the attenuation and deflection suffered by an electron beam when it passes through a carbon conductive coating and an oxide film layer on the surface of bulk samples are studied by Monte Carlo simulations and energy dispersive spectroscopy with electron excitation. Analytical expressions are provided for the primary beam energy and intensity losses and for the deflection of the incident electrons in both layers, in terms of the incidence energy, the film mass thicknesses, and the atomic number of the oxidized element. From these analytical expressions, suitable corrections are proposed for the models used to describe the X-ray spectrum of the substrate, including also the contribution of the X-rays generated in the oxide and conductive films and the characteristic X-ray absorption occurring in those layers. The corrections are implemented in a software program for spectral analysis based on a routine of parameter refinement, and their influence is studied separately in experimental spectra of single-element standards measured at different excitation energies. Estimates for the layer thicknesses are also obtained from the spectral fitting procedure.

L-shell transition rates for Ba, Ta, W, Pt, Pb and Bi using electron microprobe

a ´´ ´ ´ (5000) Cordoba, Argentina ´ Abstract L-shell transition rates for several elements are obtained by means of a method for refining atomic and experimental parameters in electron probe microanalysis. An analytical function is used to account for the bremsstrahlung, characteristic peaks and detection artifacts from an irradiated material. The refinement procedure consists of minimizing the differences between the experimental X-ray spectrum and that predicted by means of the function proposed. In this work, the spectra considered were recorded with an energy dispersive system. The procedure is applied to Ta, W, Pt, Pb and Bi pure samples and a BaSO sample. More than ten transitions are studied for each 4 element. The results obtained are in agreement with data given in the literature. Finally, the optimization procedure is applied to the refinement of mass concentrations in a sample in which L-lines are strongly overlapped with K lines. 2002 Elsevier Science B.V. All rights reserved.

Silver L1, L2 and L3 cross-sections for ionization and x-ray production by electron impact

The experimental determination of ionization cross-sections and total x-ray production crosssections under electron impact is carried out for the three silver L-subshells. The very complex spectral structure involving several satellite bands was previously investigated by analyzing wavelength-dispersive spectra acquired in an electron microprobe. In this work, careful spectral processing is carried out by means of the POEMA software developed previously, considering the spectral energy intervals which include the main Ag-L emissions. The resulting ionization cross-sections are compared with analytical models based on distorted wave Born approximation calculations, the experimental determinations of the present work being underestimated by these predictions. To the best of the authors’ knowledge, this is the first time these magnitudes are reported in the literature in this energy range. The total L-shell x-ray production cross-sections are also compared with the only previous experimental data found, obtained with different experimental settings.

Experimental Method to Determine the Absolute Efficiency Curve of a Wavelength Dispersive Spectrometer

A method for the experimental determination of the absolute efficiency of wavelength dispersive spectrometers was developed, based on the comparison of spectra measured with a wavelength dispersive system and with an energy dispersive spectrometer. The aim of studying this parameter arises because its knowledge is necessary to perform standardless analysis. A simple analytical expression was obtained for the efficiency curve for three crystals ~TAP, PET, and LiF! of the spectrometer used, within an energy range from 0.77 to 10.83 keV. Although this expression is particular for the system used in this work, the method may be extended to other spectrometers and crystals for electron probe microanalysis and X-ray fluorescence.

Structure of the sulfur K x-ray emission spectrum: influence of the oxidation state

The sulfur K x-ray emission was studied in pure sulfur, anhydrite (CaSO4) and sphalerite (ZnS) samples. The ionizations were induced by electron impact and the spectra were recorded with a wavelength dispersive spectrometer. The spectral processing was performed through a methodology based on the optimization of atomic and experimental parameters. Energies and intensities of diagram and satellite lines were determined for a set of transitions in the Kα and Kβ groups. The lines studied include Kα22, Kα2, Kα1, Kα � , Kα3, Kα4, Kα5, Kα6, Kβ1,3, Kβ-RAE, Kβ III , Kβ IV , Kβx, Kβ � and Kβ �� . The main spectral differences between the three oxidation states were analysed, considering the influence of the ligand atoms. The results were compared with data published by other authors and the origin of certain lines was discussed on the basis of data available in the literature.