Positron annihilation

Of the particles emitted from radioactive nuclei, the positively charged beta rays or positrons are among the least known, yet they have some remarkable properties, since they provide by far the most easily accessible examples of anti-matter. Over the last few years it has become clear that the particular combination of conventional and unconventional properties possessed by positrons makes them especially valuable as probes of microscopic and atomic scale imperfections in metals, and their use for this purpose in metallurgy is now well established. The chapter summarizes the properties concerned, considers the observational techniques required to exploit them, and presents examples of such studies, with the object of showing how they are beginning to contribute to some areas of nondestructive testing. In particular, positron annihilation shows promise as a method for detecting deformation, creep and fatigue damage in metals and alloys, where there is a dearth of adequate techniques