Theory

Abstract

To provide the basis for the detailed discussion of the experimental results in the following chapters we shall in this chapter discuss briefly the theories of positron annihilation; Ps atomic physics; and the positron and Ps states in condensed matter. Of course, detailed calculations of the measurable quantities are normally impossible or very difficult indeed to perform, except in the simplest cases. As is the case in most of condensed matter science the use of judicious approximations is essential! However, an understanding of the fundamental theoretical principles, and the fairly qualitative results which can usually be derived, must be achieved before the positron annihilation results can be interpreted, in general.