POSITRON-ANNIHILATION FOR THE NONDESTRUCTIVE ASSESSMENT OF THE EARLY STAGES OF DAMAGE

Positron annihilation gamma-ray lineshape analysis is one of the few t echniques which can provide an early warning of incipient materials de gradation in metallic components. The National NDT Centre at AEA Techn ology Harwell has developed a portable NDT system, the Positron Annihi lation Lineshape Analysis (PALA) System, which can be used to carry ou t measurements both in the laboratory and at external sites. The syste m utilises the narrowing of the annihilation gamma ray lineshape, whic h occurs if the annihilation event occurs near vacancies in the lattic e of a metal, to give information on the early stages of damage. A bri ef description of the PALA system is given, and its use to measure pla stic damage in a number of cases illustrated.