# Unusual charge exchange by swift heavy ions at solid surfaces

## TL;DR

This study uses x-ray spectroscopy to reveal unexpectedly large charge exchange phenomena at solid surfaces during swift heavy ion interactions, challenging existing models and impacting various scientific fields.

## Contribution

It uncovers a surprisingly large charge exchange process at surfaces during heavy ion interactions, validated experimentally and theoretically, which was previously unrecognized.

## Key findings

- Up to tens of electrons participate in charge exchange per event.
- Charge exchange at surfaces is significantly larger than bulk processes.
- Implications for astrophysics, materials science, and medical physics.

## Abstract

We have employed x-ray spectroscopy to probe the charge changing process only in the bulk of the foil when swift heavy ions pass through it. In contrast, the electromagnetic methods take into account integral effect of the charge changing process in the bulk as well as the charge exchange phenomenon at the surface of the foil. Thus, the difference between the mean charge states so measured from the two methods disentangles the charge exchange phenomenon at the surface from the charge changing process in the bulk and, provides opportunities to refine the understanding of ion-surface interactions. Very surprisingly, up to tens of electrons per event participate in the charge exchange phenomenon during swift heavy ion-surface interactions. This finding has been validated with a series of experiments using several ions (z = 22-35) in the energy range of 1.5-3.0 MeV/u and also verified theoretically with Fermi-gas model. Interestingly, such unusual charge exchange phenomenon could play significant role in x-ray emission of many astrophysical environments, infrared emission bands from range of environments in galaxies, accelerator physics, ion energy losses in solids, heavy ion cancer treatments, inner shell ionization by heavy ions, and surface modifications in nano scale.