Positron Annihilation for the Non-Destructive Assessment of the Early Stages of Damage

Abstract
Positron annihilation γ-ray lineshape analysis is one of the few techniques which can provide an early warning of incipient materials degradation in metallic components. The National NDT Centre at AEA Technology Harwell has developed a portable NDT system, the Positron Annihilation Lineshape Analysis (PALA) System, which can be used to carry out measurements both in the laboratory and at external sites. The system utilises the narrowing of the annihilation gamma ray lineshape, which occurs if the annihilation event occurs near vacancies in the lattice of a metal, to give information on the early stages of damage. A brief description of the PALA system is given, and its use to measure plastic damage in a number of cases illustrated.