IFEG   20353
INSTITUTO DE FISICA ENRIQUE GAVIOLA
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Experimental determination of atomic parameters involving decays to the K shell
Autor/es:
ALEJO CARRERAS; S. P. LIMANDRI; R. D. BONETTO; J. C. TRINCAVELLI
Lugar:
Cabo Frio, Rio de Janeiro, Brasil
Reunión:
Congreso; XI Seminario Latinoamericano de Análisis por Técnicas de Rayos X (SARX 2008); 2008
Institución organizadora:
Comité organizador SARX 2008
Resumen:
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K-shell X-ray emission induced by
electron impact was studied for elements with atomic number between 12 and 30.
The spectra were measured for incidence energies in the range 3-30 keV, with a
scanning electron microscope equipped with a wavelength dispersive
spectrometer.
Relative
transition probabilities and natural linewidths were obtained for several
transitions. In addition, X-ray production cross-section values were determined.
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:
where N is the number of channels in the spectral region of interest, P is the number of parameters fitted, Ĩi and Ii are respectively the predicted and experimental
intensities for the energy Ei
corresponding to the 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 implemented
[3].
The results agree with experimental
[4] and theoretical [5] data published by other authors, in most of the
analyzed cases, considering the combined uncertainties.
Keywords: X-ray spectroscopy; relative
transition probabilities; natural linewidths
References:
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.