Untitled

Abstract

The ionization of atomic shells by the impact of spin-½ charged particles in collisions involving large momentum transfers is analysed within the framework of the relativistic plane-wave Born approximation. An expression is derived for the double differential cross section based on the impulse approximation, which leads to a relationship between the generalized oscillator strength and the Compton profile. The agreement between the impulse and plane-wave Born approximations is then improved by introducing a Born Compton profile extracted from the numerically evaluated (Born) generalized oscillator strength. Calculations corresponding to the Bethe ridge of different atomic shells demonstrate the usefulness of the present approach for obtaining accurate generalized oscillator strengths at large momentum transfers with a minimum of numerical effort.

Monte Carlo simulation of x-ray spectra generated by kilo-electron-volt electrons

“…In the energy range of interest, DWBA calculations are formidably difficult, not only because of the very slow numerical convergence of the partial-wave series, but also because radial integrals must be calculated with high accuracy to prevent the accumulation of numerical errors. The calculation program of Segui et al 17 overcomes these difficulties and reproduces experimental ionization cross section measurements of both K and L shells satisfactorily, as has been recently shown 18,19 for selected elements.…”

“…Here, we will adopt the DWBA cross sections computed by Segui et al. 17 To give a feel for the reliability of these DWBA ionization cross sections, in Fig. 1 we compare results from experimental measurements of K-shell ionization cross section for Fe and L␣ x-ray production cross section ( L␣ ) for Au, with DWBA calculations.…”

“…We assume that the atomic relaxation process is independent of the mechanism by which the initial vacancy is created. In the simulation code, the relaxation of innershell vacancies is followed until the K and L shells are filled up, i.e., until the vacancies have migrated to M and outer 17 Symbols are experimental data from different sources. 19,[30][31][32][33]25,35 shells.…”

“…16 Segui et al, 17 on the other hand, have developed a computer code for calculating electron-impact ionization cross sections of neutral atoms using the distorted-wave Born approximation ͑DWBA͒. In the energy range of interest, DWBA calculations are formidably difficult, not only because of the very slow numerical convergence of the partial-wave series, but also because radial integrals must be calculated with high accuracy to prevent the accumulation of numerical errors.…”

“…17 The relaxation of ionized atoms is simulated by using transition probabilities from the Lawrence Livermore National Laboratory Evaluated Atomic Data Library ͑EADL͒. 20 As in our previous studies, the transport of electrons and photons is described by the standard, detailed method using the latest version of the general-purpose MC code PENELOPE.…”