The Impact‐Parameter Dependence of Electron Stopping in Proton Collisions with Gas and Solid Atoms

Abstract

The semiclassical approximation with rectilinear trajectory is used to calculate the impactparameter dependence of electronic stopping for fast-proton collisions with gas and solid atoms. The effects arosen from electron shell rearrangement and dynamic screening of proton charge in a solid, on the electron stopping are studied for case of solid targets. The calculation results are compared with experimental data and with approximate calculations based on sum rules and local electron density approximation.Eine halbklassische Naherung mit gerader Trajektorie wird benutzt, um die Abhiingigkeit des StoBparameters der elektronischen Bremsung bei StoBen schneller Protonen mit Gas-und Festkorper-Atomen zu berechnen. Die aus der Umordnung und der dynamischen Abschirmung der Protonenladung in einem Festkorper herruhrenden Einfliisse auf die Elektronenbremsung werden im Fall der Festkorpertargets untersucht. Die berechneten Ergebnisse werden mit experimentellen Werten und mit Naherungsberechnungen verglichen, die auf der Summenregel und der Niiherung der lokalen Elektronendichte beruhen.

Asymmetric line shapes for medium energy H and He ions undergoing a large-angle collision

“…This is due to constraint that the gas target should be dilute enough to suppress multiple scattering and to keep an ultrahigh vacuum ͑UHV͒. For small-angle forward scattering ͑scattering angle: a few mrad͒, however, Auth and Winter 21 observed beautiful line shapes involving elastic and inelastic components using medium energy proton beams and had good agreement between their observation and the first-order perturbation 22 in the mean energy loss and straggling. In order to view the line shapes for a large-angle scattering, it is essential to prepare characteristic surfaces such as adatoms or substrate structures.…”

“…Based on first-order perturbation theory, Kabachnik et al 22 calculated impact-parameter ͑b͒ dependent electronic energy loss Q͑b͒ assuming a straight ion trajectory. Using the much more reliable coupled-channel method, 18,27 we solve the following timedependent Schrödinger equation for one active electron:…”

Monte Carlo Simulation Analysis of Proton‐Energy Spectra for Axial Channeling in Silicon in the Intermediate Energy Region

“…The interaction between the incident particle and the core electrons is given by a Coulomb potential screened by the valence electron gas. More details of this calculation are given in [28].…”

Random and channeling stopping powers of He and Li ions in Si

“…In fact, the reduction of the stopping power for channeled ions is due to a significant suppression of collisions with small impact parameters. Full calculations of the impact-parameter-dependent energy loss using first-order perturbation theory have been performed only recently, 22 followed later by the first coupled-channel calculations. 23,24 These calculations are time consuming and results are available only for a few selected collision systems.…”