BUSCADOR RECOLECTA

A generalization of curves of growth called CSigma (Cσ) graphs, which allows including several lines of various elements in the same ionization state at different concentrations, is proposed for laser-induced breakdown spectroscopy (LIBS) experiments. The method relies on the Boltzmann, Saha and radiative transfer equations for plasmas in local thermodynamic equilibrium. Cσ graphs are based on the calculation of a line cross section σl for each of the experimental data, starting from the atomic data of the line, the temperature and the electron density. A model of homogeneous plasma, applied separately for neutral atoms and ions, is used. A limit of validity is established for this model. Experimental Cσ graphs have been obtained using fused glass samples containing Fe, Mn, Mg, Si and Cr. By fitting experimental Cσ graphs to calculated curves, the LIBS system becomes characterized by a set of four parameters βA, Nl, T, Ne, different for neutral atoms and ions. Starting from this characterization, the intensity and self-absorption of a given spectral line of an element at a certain concentration may be predicted, provided that its atomic data are known and the limit of validity is not exceeded., This work has been supported by the project FIS2011-29521 of the Spanish Ministerio de Economía y Competitividad.

Stark widths and shifts of Cr II lines with wavelengths in the range 2000–3500 Å have been determined by laser-induced breakdown spectroscopy. The spectra have been measured at different instants of the plasma evolution from 0.6 to 3.4 μs, at which the temperature and electron density are in the ranges 12 000–16 300 K and (0.89–8.2) × 10¹⁷ cm ˉ³, respectively. The laser-induced plasmas have been generated from three fused glass samples with different chromium concentrations, selected to control the self-absorption of the lines. The Stark widths and shifts are compared with the experimental and theoretical data available in the literature., This work has been supported by the project FIS2011-29521 of the Spanish Ministerio de Economia y Competitividad.

We propose a method for determination of transition probabilities by laser-induced breakdown spectroscopy that avoids the error due to self-absorption. The method relies on CSigma graphs, a generalization of curves of growth which allows including several lines of various elements in the same ionization state. CSigma graphs are constructed including reference lines of an emitting species with well-known transition probabilities, together with the lines of interest, both in the same ionization state. The samples are fused glass disks prepared from small concentrations of compounds. When the method is applied, the concentration of the element of interest in the sample must be controlled to avoid the failure of the homogeneous plasma model. To test the method, the transition probabilities of 9 Ca II lines arising from the 4d, 5s, 5d and 6s configurations are measured using Fe II reference lines. The data for 5 of the studied lines, mainly from the 5d and 6s configurations, had not been measured previously., This work has been supported by the project FIS2011-29521 of the Spanish Ministerio de Economía y Competitividad.