Positrons as Solid State Probes

The phenomenon of low energy positron-electron annihilation provides the basis for a wide variety of sensitive and significant studies of particle, atom, and materials problems. The breadth of the field can best be gauged from the many recent and excellent books and reviews describing works concerning fundamental tests of quantum electrodynamics [1], positronatom scattering in gases [2], positron and positronium chemistry [3], solid state physics [4,5,6,7], metallurgy [8,9], and medical physics [10]. The subject is clearly too large for complete cover by a single author within these proceedings. Accordingly we shall in this paper concentrate our attention on those studies in solids where the positron has proved a particularly powerful probe of the physics of the medium. The physics of the positron will be considered only to the degree that is necessary to establish its credibility as such a probe.