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

The Si $K$ x-ray production cross sections for ${\mathrm{F}}^{q+}\mathrm{}(q=3-9\mathrm{})\mathrm{}$ 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 ($\tilde{\omega }=1.5\mathrm{}{\omega }_0$, where ${\omega }_0$ is the fluorescence yield for an atom with single $K$ vacancy) determined from high-resolution x-ray spectra and configuration fluorescence yields. For ${\mathrm{F}}^{q+}$ ($q\le 6$) 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 ${\mathrm{F}}^{9+}$ ions and those for ${\mathrm{F}}^{q+}$ ions ($q\le 6$). 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.