A Doppler broadening positron annihilation technique for the study of defects in bulk samples

A Doppler broadening positron annihilation technique which allows for the study of near surface defects in bulk samples is described. The method is capable of observing changes in the homogeneous bulk defect concentration in a sample and is also able to characterize spatially localized near-surface defects in bulk materials with a resolution of about 1 mm. The applicability of this method is demonstrated by measurements on a sample of polycrystalline aluminum into which defects have been introduced by mechanical deformation. Isochronal annealing studies have been used to characterize the defect recovery in this material and are compared with results of conventional Doppler broadening measurements.