Track formation and electron emission in swift ion collisions with condensed matter

Abstract

Electron ejection from target atoms is one of the basic processes when ionizing radiation interacts with matter. The primary electrons and their subsequent secondary interactions lead to the deposition of energy around the ion trajectory. The detailed knowledge of the structure of these ion tracks is a key issue for our understanding of radiation effects in condensed matter, an important example being calculations of the RBE of heavy particles, where doubly differential electron ejection cross sections are a key input parameter. Usually, data obtained from single collisions, i.e. with gas targets, are used, but condensed matter effects may considerably alter the emission patterns. Therefore, we will focus on the primary ionization (binary encounter and soft electron emission), which is common to single atoms (gas targets) and condensed matter. Then, special emphasis will be given to discuss effects, which are only seen in condensed matter (electron transport and multiple scattering effects, jet-like structures, wake effects due to collective excitation of plasmons), but not in gaseous targets (single collisions).