Few Body Effects in the Electron and Positron Impact Ionization of Atoms

R.I Campeanu,Colm T Whelan

doi:10.3390/atoms9020033

Abstract

Triple differential cross sections (TDCS) are presented for the electron and positron impact ionization of inert gas atoms in a range of energy sharing geometries where a number of significant few body effects compete to define the shape of the TDCS. Using both positrons and electrons as projectiles has opened up the possibility of performing complementary studies which could effectively isolate competing interactions that cannot be separately detected in an experiment with a single projectile. Results will be presented in kinematics where the electron impact ionization appears to be well understood and using the same kinematics positron cross sections will be presented. The kinematics are then varied in order to focus on the role of distortion, post collision interaction (pci), and interference effects.

Highlights

In a coincidence experiment, a projectile of momentum k0, energy E0 impinges on a target atom and ionizes it
The physics underlying the form of the Triple differential cross sections (TDCS) are understood in terms of a simple model [26] in which the target electron is assumed to be at rest relative to its nucleus, and the ionization process is viewed as a free collision between the incident and target electron
We find that, for high impact energies, the distorted wave Born approximation (DWBA) theory correctly reproduces the experimental results

Summary

Introduction

A projectile of momentum k0 , energy E0 impinges on a target atom and ionizes it. Born approximation, being symmetric about the direction of momentum transfer with the only significant structures coming from target wave function effects [4]. In these kinematics, it is difficult to disentangle the different few body contributions [5,6]; this problem is enhanced because what few differences there are tend to be in the absolute size of the cross section which is extremely demanding to measure accurately [7]. The DWBA has provided excellent agreement with electron impact ionization in energy sharing kinematics and, because of its relative simplicity and flexibility, is an ideal vehicle to explore positron scattering and the different few body mechanisms

Electron Impact

Positron Scattering

Coplanar Symmetric Geometry

Non Coplanar Energy Sharing Geometries

Energy Sharing Perpendicular Plane Geometry

Conclusions