Cross Sections For K-shell Ionization Of Atoms Research Articles

Electron impact ionization cross-section of K-shell and H- to Be-isoelectronic series: An empirical model

The model of Cengiz (2002) [Approximate inelastic scattering cross sections of electrons. Rad. Phys. Chem. 65, 33–44] has been modified by incorporating both the ionic and relativistic corrections due to Uddin et al. (2006) [Modified Kolbensvedt model for the electron impact K-shell ionization cross-sections of atoms and ions. Eur. Phys. J. D 37, 361–369.] to investigate the electron impact s-orbital ionization in the K- and L-shells. With a single set of species independent parameters our evaluated inner shell ionization cross section of atomic targets from H to U over incident energies up to 2GeV and of H- to Be-isoelectronic series reproduce the experimental findings nicely.

Modified Kolbensvedt model for the electron impact K-shell ionization cross-sections of atoms and ions

A modification of the Kolbensvedt model, MKLV, in terms of ionic, correlation (between the incident and target electrons) and relativistic corrections, is proposed to calculate the K-shell electron impact ionization cross-sections of neutral and ionic targets. The modified model, with a single set of parameters, is found to reproduce satisfactorily the experimental data for the neutral H, Al, Ar, Mn, Ge, Mo, Ag, Sn, Au, Bi and U and ionic Li+, B4+ and O7+ targets better than the existing empirical models from threshold energies to as high as 104 MeV. For the Ag target, the calculations from MKLV follow closely the results of Scofield, and for Au, those of Scofield, and Ndefru and Malik, both done in the relativistic Born approximation with the Moller interaction, at energies higher than the peak region.

Some recent progress on the measurement of K-shell ionization cross-sections of atoms by electron impact: Application to Ti and Cr elements

In this paper, we have taken some measures to improve the accuracy of our experimental data for K-shell ionization cross-sections by electron impact. These measures include (1) measurement of the thin target thickness with Rutherford backscattering spectroscopy and (2) detection efficiency calibration in the lower energy region using thick carbon target bremsstrahlung by electron impact and (3) electron reflection correction and electron mean track length correction based upon Monte Carlo method. These measures are applied to the measurement of K-shell ionization cross-sections of Ti and Cr elements from the threshold energies up to 26 keV. From the comparison with some theoretical models, empirical formulae and some previous experimental data, it is concluded that these measures taken in this paper are effective in the improvement of accuracy of experimental data. The present experimental data for Ti and Cr elements also clarify the discrepancies among some experimental data sets. In addition, these measures will also be very helpful in the measurement of K-shell ionization cross-sections for lower Z elements and in the measurement of L, M-shell ionization cross-sections for medium and higher Z elements.

Ionization cross-sections of molecules due to electron impact

Recently, Mayol and Salvat have employed a semi-phenomenological approximation along with the first Born approximation to calculate K-shell ionization cross-sections of atoms. Their method requires optical oscillator strengths (OOS) as input instead of the generalised oscillator strengths (GOS). As the generation of the GOS for molecules is a difficult task, in the present paper we have extended the semi-phenomenological approximation of Mayol and Salvat to investigate molecular ionisation because of the availability of OOS for a large number of molecules. Cross-sections for the total ionisation and for the formation of the parent ions of H 2, N 2,O 2, NH 3, H 2O and CO 2 by electron impact are calculated in a modified first Born approximation for the incident energy E varying from the threshold of ionisation to 1 keV. The contribution of the exchange is included through the Ochkur approximation. Dissociative ionisation cross-sections of NH 3, H 2O and CO 2 giving rise to NH 2 +, OH + and O + ions, respectively, have also been evaluated. The calculated cross-sections are, in general, in good agreement with the experimental data over a wide energy range ( E ⪖ 50 eV) and the same holds for ratios of the partial to the total ionisation cross-sections.