Significance of the high charge state of projectile ions inside the target and its role in electron capture leading to target-ionization phenomena

Abstract

The $K$ x-ray spectra of different targets (Cu, Zn, and Ge) induced by 3--5 MeV/u Si projectile ions have been measured to determine the $K$-shell ionization cross section. A significant difference is observed between the measurements and theoretical estimates, with the latter being about 50% below the experimental results. This underestimation is attributed to the charge exchange from the target $K$ shell to projectile $K$ and $L$ shells. Such an observation can only be possible if the projectile ions attain up to H- and He-like charge states. Corresponding projectile charge state fractions have been evaluated from the Lorentzian charge state distribution, where the mean charge state is taken from the Fermi gas model [W. Brandt et al., Phys. Rev. Lett. 30, 358 (1973)] and the width from the Novikov and Teplova approach [Phys. Lett. A 378, 1286 (2014)]. The sum of the direct ionization cross section and $K\text{\ensuremath{-}}K+K\text{\ensuremath{-}}L$ capture cross sections gives a good agreement with the measured cross sections. Furthermore, we have validated this methodology with available data for a Si ion on Ti target. Such results may be useful in many solid target-based applications.