Electronic Equilibrium and Transition Stages

Abstract

The concept of electronic equilibrium is presented in its general aspects. Absolute equilibrium requires conditions which are not fulfilled for high-energy photon beams, but a transient equilibrium can be considered. The influence function is used to introduce the concept of a practical equilibrium. Transition stages at a plane interface perpendicular to the beam direction are dealt with by a simplified form of the influence function, reduced to one parameter. Some particular conditions are considered for which experimental data are available, e.g. interface between vacuum and medium, interface between low-density and high-density media, and the interface between media of different atomic composition.