Inner Shell Ionization Processes

Abstract

In this paper I would like to consider some aspects of electron impact ionization from atomic inner shells. I will be particularly interested in the theoretical understanding of coincidence measurements, i.e. the (e, 2e) process. Fundamentally an (e, 2e) experiment is one where an electron, of well-defined energy and momentum, is fired at a target, ionizes it and the two exiting electrons are detected in coincidence. The energies and positions in space of these electrons are determined by the experiment so in effect all but the spin quantum numbers are then known. We can, therefore, describe it as a kinematically complete experiment; if we could also measure all the spins we would have all the information on a scattering experiment that quantum mechanics will allow. The technique offers both the possibility of a direct determination of the target wavefunction and profound insights into the nature of few body interactions. What information you extract from such an experiment really depends on the kinematics you choose and the target you use. Integrated cross sections can be crude things and you need the full power of a highly differential measurement to tease out the delicacies of the interactions. Indeed often the most intriguing effects turn up in peculiar geometries where the cross sections are small and where a number of relatively subtle few body interactions are at play.