María Cecilia Valentinuzzi

X-ray resonant Raman scattering cross sections of Mn, Fe, Cu and Zn

X-ray fluorescence spectra present singular characteristics produced by the different scattering processes. When atoms are irradiated with incident energy lower and close to an absorption edge, scattering peaks appear due to an inelastic process known as resonant Raman scattering. It constitutes an important contribution to the background of the fluorescent line. The resonant Raman scattering must be taken into account in the determination of low concentration contaminants, especially when the elements have proximate atomic numbers. The values of the mass attenuation coefficients experimentally obtained when materials are analysed with monochromatic x-ray beams under resonant conditions differ from the theoretical values (between 5% and 10%). This difference is due, in part, to the resonant Raman scattering. Monochromatic synchrotron radiation was used to study the Raman effect on pure samples of Mn, Fe, Cu and Zn. Energy scans were carried out in different ranges of energy near the absorption edge of the target element. As the Raman peak has a non-symmetric shape, theoretical models for the differential cross section, convoluted with the instrument function, were used to determine the RRS cross section as a function of the incident energy.

Determination of the oxidation state by resonant-Raman scattering spectroscopy

X-Ray fluorescence spectra present singular characteristics produced by the different scattering processes. When atoms are irradiated with incident energy lower and close to an absorption edge, scattering peaks appear due to an inelastic process known as resonant Raman scattering (RRS). In this process, the emitted photons have a continuous energy distribution with a high energy cut-off limit. This work presents results regarding the possibility of determining the oxidation state by resonant Raman scattering using an energy dispersive system. Pure samples of transition metals (Cu, Fe, Mn) and different oxides of them (CuO, Cu2O, Fe2O3, Mn2O3, MnO2) were irradiated with monochromatic synchrotron radiation below their absorption edges to inspect the RRS emissions. The spectra were analyzed with specific programs using non-conventional functions for data fitting and a FFT smoothing procedure was applied. After smoothing, the RRS residuals are studied in order to detect variation with respect to the theoretical curve. These variations are closely related with the chemical environments of the absorbing element and can provide relevant structural information of the sample. The changes existing in the RRS structure between pure elements and their oxides are clearly discriminated and suggest the possibility of structural characterization by means of resonant Raman scattering using an energy-dispersive system combined with synchrotron radiation.

3D scanning electron microscopy applied to surface characterization of fluorosed dental enamel

The enamel surfaces of fluorotic teeth were studied by scanning electron stereomicroscopy. Different whitening treatments were applied to 25 pieces to remove stains caused by fluorosis and their surfaces were characterized by stereomicroscopy in order to obtain functional and amplitude parameters. The topographic features resulting for each treatment were determined through these parameters. The results obtained show that the 3D reconstruction achieved from the SEM stereo pairs is a valuable potential alternative for the surface characterization of this kind of samples.

Qualitative microanalysis of calcium local structure in tooth layers by means of micro-RRS

The Resonant inelastic X‐ray scattering or resonant Raman scattering is an inelastic process of second order that becomes important when the energy of the excitation radiation is below but close to an absorption edge. In this process, the emitted photons have a continuous energy distribution with a high energy cut‐off limit. In the last few years, experiments of resonant Raman scattering has become a very powerful technique to investigate excitations of electrons in solids. A qualitative study of the calcium local structure in the different layers of teeth was carried out. In order to perform the analysis, several measurements of tooth samples were achieved using monochromatic synchrotron radiation at the XRF station of the D09B‐XRF beamline at the Brazilian synchrotron facility (LNLS, Campinas), below and close to the K absorption edge of Ca to inspect the resonant Raman scattering spectra. First of all, the spectra were analyzed with specific software to fit the experimental data. After that, the residuals were determined and a  fast Fourier transform smoothing procedure was applied, taking into account the instrument functions of the detecting system. These oscillations present patterns that depend of the tooth layer, i.e. of the calcium state.

Theoretical calculations of the influence of resonant Raman scattering on the quantification of XRF spectrochemical analysis

In this work we present theoretical calculations of the resonant Raman scattering contributions to the background of X-ray fluorescence spectra. The main goal of the paper is to obtain a simple and reliable procedure to calculate the influence of RRS in spectrochemical analysis by X-ray fluorescence including second order enhancement processes. In order to perform the calculations, the Shiraiwa and Fujino model was used to calculate the characteristic intensities of the different atomic processes involved. In the case of polychromatic excitation over a multi-element sample of proximate atomic numbers, the calculations show that the contribution of RRS is higher than Compton scattering but lower than coherent scattering, this last process being the most important source of background in the range of the fluorescent lines. The calculated effects of enhancements are rather low and have influence only on the lightest elements of the spectra. On the other hand, the resonant Raman scattering line interferes with fluorescent peaks in the case of monochromatic excitation when elements of proximate atomic numbers are analyzed (for example Al–Si). The model proposed here allows the analysis of the different sources of background, which contribute to a better understanding of the physical processes involved in the different techniques of XRF analysis. In addition, the calculations presented here can contribute significantly to a more precise quantification of traces and minor components.