Si K -shell ionization and electron transfer cross sections: Solid targets

The Si K x-ray production cross sections for Fq+(q=3-9) ion impact in the energy range of 0.4-2.2 MeV/amu are determined in the limit of a vanishingly thin target from the observed target thickness dependence of the x-ray yields. The ionization cross sections are deduced from the measured x-ray production cross sections using an average fluorescence yield (̃ \~ω=1.5ω₀, where ω₀ is the fluorescence yield for an atom with single K vacancy) determined from high-resolution x-ray spectra and configuration fluorescence yields. For Fq+ (q≤6) ion impact, the measured ionization cross sections are compared with the plane-wave-Born-approximation prediction with and without the Coulomb deflection and increased-binding-energy effects. The Si K shell to F K shell electron-transfer cross sections are determined from the difference between the ionization cross sections for F⁹⁺ ions and those for Fq+ ions (q≤6). The results are compared with the prediction based on the two-state atomic-expansion method and that based on the modified Oppenheimer-Brinkman-Kramers approximation. A comparison is also made between the Si solid-target measurements with those obtained for gaseous Ne and Ar gas targets. The solid-target and gas-target data are consistent at 1.58 MeV/amu. Finally, from a comparison between the measured equilibrium x-ray yields and the calculated x-ray yields using the equilibrium charge distribution of projectiles after passing through foils, it is found that the projectiles have a considerably larger number of K-shell vacancies inside solids than after passing through solids at lower-impact energies.