Experimental determination of atomic parameters involving decays to the K shell.

CARRERAS A; LIMANDRI S.; BONETTO RD; TRINCAVELLI J.

Cabo Frio, Rio de Janeiro, Brazil

Congreso; XI Latin American Seminary of Analysis by X-Rays Techniques; 2008

X-ray spectra excited by electron impact were studied from elements with atomic number between 13 and 30. The spectra were measured for incidence energies in the range 3-30 keV, with an electron microscope equipped with a wavelength dispersive spectrometer.Relative transition probabilities and natural linewidths were obtained for several K transitions. In addition, X-ray production cross-section values were obtained. This parameter, defined as the product of the fluorescence yield and the ionization cross-section, depends on the electron energy. For this reason, spectra produced with different excitation energies were investigated. The mentioned parameters were obtained by spectral fitting performed by means of the optimization routine implemented in the software POEMA[1]. This method consists in minimizing the differences between an experimental spectrum and an analytical function proposed to predict it, which takes into account characteristic peaks, bremsstrahlung and different detection artifacts. Thus, the quantity to be minimized is: chi2 = (1/(N-P)) Sum(I´i-Ii)^2/Ii  where N is the number of channels in the spectral region of interest, P is the number of parameters fitted, I´i and Ii are respectively the predicted and experimental intensities for the energy Ei of channel i. Characteristic emission was taken into account by considering the so-called ZAF corrections, with a line profile given by a Voigt function, whereas an empirical model was used for the prediction of bremsstrahlung [2]. For the detection efficiency of the spectrometer, a model developed previously was used [3].The results, compared with experimental [4] and theoretical [5] data published by other authors, agrees in most of the analyzed cases, considering the combined uncertainties.Keywords: X-ray spectroscopy; relative transition probabilities; natural linewidthsReferences:1. BONETTO R.; et al. “Optimization of parameters in electron probe microanalysis”, X-Ray Spectrom., v. 30, p. 313-319, 2001.2. TRINCAVELLI J.; CASTELLANO G. “The prediction of thick target electron bremsstrahlung spectra in the 0.25-50 keV energy range”, Spectrochim. Acta B, v. 63, p. 1-8, 2008.3. TRINCAVELLI, J.; et al. “Experimental method to determine the absolute efficiency curve of a wavelength dispersive spectrometer”, Microscopy and Microanalysis, in press.4. Handbook of Chemistry and Physics, CRC Press, Editor D. Lide, 74th edition, 1994.5. SCOFIELD, J. “Exchange corrections of K x-ray emission rates”, Phys. Rev. A, v. 9, p. 1041-1049, 1974.