Positron Studies of Lattice Defects in Metals

Abstract

The conscious study of lattice defects with positrons is now some ten years old. Although sharing the techniques and guided by the results of the longer established studies described in Chap.2, defect studies are based on a somewhat different philosophy. Electronic structure studies rely for their credence on a belief that, in sufficiently well-annealed single-crystal samples, the positrons annihilate from a common, well-defined, and delocalised state in which they can freely sample nonlocal properties of the medium. The perturbing effect of the positron charge on the electronic system is in general an unwelcome complication. In defect studies the-situation is radically different. Here the charged positron’s interactions with the surrounding medium play the vital role in providing for the possibility of a variety of additional localised positron states at the structural defects. The investigation of defect-induced changes in the commonly measured characteristics of annihilation (Chap.l) and the interpretat on of such changes in terms of such things as the concentration, nature, and origins of the defects responsible are the essential ingredients of our study.