ABSTRACT
This chapter describes the electromagnetic interactions of a charged particle with a medium and the interactions of virtual photons with that medium. The rate at which a charged particle loses energy may be calculated for a classical transfer of energy to free electrons through the Coulomb interaction, as in the original papers of Bohr. For particles with very high velocity there is the possibility that the particle may actually be travelling faster than the phase velocity of the photons, which gives rise to cherenkov radiation. When a charged particle passes through matter, the exchange processes involved in the energy loss occur via photons having a wide range of energies. The Landau distribution is distinctly asymmetrical and consequently the most probable energy loss, which is given by the peak of the distribution, is less than the mean energy loss.
