Alejo C. Carreras

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.

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.

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.

Structure of the Ru, Ag and Te L X-ray emission spectra

The emission of X-rays in atomic transitions from L-shell vacancy states of Ru, Ag and Te induced by electron incidence was studied. To this end, L X-ray spectra were measured with a wavelength dispersive spectrometer, and processed by a parameter optimization method previously developed. A large set of atomic parameters corresponding to diagram transitions, such as relative transition probabilities, characteristic energies and natural linewidths of the three elements, were determined. The results obtained are compared to the data found in the literature, when available. In general terms a good agreement was observed, supporting recent calculations based on the framework of the relativistic many-body problem in atoms. Spectral structures related to satellite and radiative Auger emissions were also analyzed, and energy shifts and relative intensities were determined. Many of these parameters were determined for the first time, which was possible due to the robustness of the spectral processing method used, even in the cases of peak overlapping and weak transitions.

Structure of the Fe and Ni L X-ray spectra

Fe-L and Ni-L X-ray spectra induced by electron impact were analyzed. The measurements were made on bulk samples using a commercial wavelength dispersive spectrometer, and the spectra were processed with a parameter optimization method previously developed. This procedure allowed for the determination of characteristic energies, relative transition probabilities and natural linewidths. The results obtained are compared to the data found in the literature, when available. Satellite and radiative Auger emissions were also analyzed, energy shifts and relative intensities being determined. Many of these parameters were determined for the first time, which was possible due to the robustness of the spectral processing method used. The line profile introduced here takes into account the differential attenuation at both sides of the absorption edge.

Measurement of K-line transition rates for Ti, V, Cr, Mn, Fe and Co using synchrotron radiation

Abstract Transition rates were obtained from spectra for pure metallic samples of atomic number ranging from 22 to 27, measured with monochromatic incident X-ray beams from a synchrotron source. The experimental setup for this consisted of an energy dispersive spectrometer in a conventional 45–45° geometry, mounted in an evacuated chamber. Absorption, detector efficiency and multiple scattering were taken into account. The results obtained are compared with recent theoretical and experimental data as well as with the well-known theoretical predictions from Scofield.