Experimental study of K-shell ionization of low-Zsolids in collisions with intermediate-velocity carbon ions and the local plasma approximation

Abstract

K-shell vacancy production in low-atomic-number (Zt = 17–29) solid targets has been measured in collisions of highly charged carbon ions with energies of 1.5–6 MeV u−1. The K-shell ionization cross sections of Cl, K, Ti, Fe and Cu are derived from the measured K x-ray cross sections. The present data-set has been used to test the predictions of a theoretical model based on the local plasma approximation (LPA). This theory takes into account the response of solid core electrons working within the dielectric formalism. We find that this ab initio ion–solid model gives very good agreement with the measured data for Fe and Cu targets, while it tends to under-estimate the data for the most symmetric collision systems studied here. We discuss the range of validity of the LPA in terms of the symmetry parameter and the impact velocity. On the other hand, a model based on the perturbed stationary state approximation, designed for ion–atom collisions (ECPSSR) is found to give excellent agreement with the measured data for all target elements over the whole energy range. All the measured cross sections for different targets are found to follow a universal scaling rule predicted by the ECPSSR.

Many-electron model for multiple ionization in atomic collisions

“…The seminal developments on the local plasma approximation (LPA) were made during the 1960s and 1970s [34][35][36][37]. However, the present SLPA introduces modifications on the original formalism based on the shell-to-shell treatment [16,17,38], and it has already been employed in the calculation of total ionization cross sections of gas and solid targets [16,[39][40][41][42] with good results.…”

Energy loss of helium ions in zinc

“…The spatial-dependent densities n s ͑r͒ of each shell of Zn (i.e., 1s, 2s, 2p, 3s, 3p, and 3d) are obtained from the atomic Hartree-Fock wave functions [24], following previous works in which the LPA showed very good agreement with experimental data [22,23,25,26]. We calculate the contribution of each shell of target electrons separately, and the total innershell energy loss as the addition of these contributions (shell to shell).…”

K-shell ionization of low Z elements in ion–solid collisions and applicability of local plasma approximation

“…In such collision systems the solid-state effect, which arises from the large electron density fluctuation and plasmon excitation, is known to influence the atomic collision processes, as evident from many experimental results in the past [see Refs. 24 to 31 in Kadhane et al (2003b)]. Most of the studies on atomic collisions with solids are related to the interaction of the ion with the free electron gas (FEG).…”