Positron annihilation; NDE at the atomic level

This paper discusses positron annihilation (PA) a versatile measurements technique that can be used for nondestructive evaluation (NDE) of many materials, including superalloys, polymers, electro-optic materials, and piezoelectric materials. PA detects atomic defects at levels well below the resolution of most other NDE methods. It is sensitive to minute changes in materials, and can be used as a tool to monitor these changes either during manufacturing or during the lifetime of parts. PA testing, however, is sensitive enough to detect these tiny defects because the annihilation characteristics of positrons are related to the electron distribution in materials. Positrons are trapped at lattice defects, where they combine with electrons and the positron/electron pair subsequently is annihilated. PA evaluation detects gamma ({gamma}) rays produced in the mutual annihilation to locate the material defect. Another advantage of PA is that it does not require special sample preparation, such as the thin sections needed for transmission electron microscopy (TEM).