Doppler-broadening measurements of polycrystals were performed in situ during tensile tests, and after various degrees of deformation. The limit of sensitivity of positrons to the defects which were produced by plastic deformation was found to occur at a resolved shear stress of 4MPa in Al and at 9MPa in Cu. These values corresponded to dislocation densities of between 2 x 1012 and 3 x 1012/m2. The temperature-dependent Doppler-broadening measurements revealed distinct differences in the positron trapping at dislocations in Cu after low and high plastic deformation. A transition in the trapping behavior occurred between 20 and 30MPa. No such dependence of the positron trapping behavior upon the degree of deformation was observed in Al. The measurements were analyzed in terms of a 3-state trapping model which provided numerical values for the trapping rates and binding energies of positrons at dislocation lines.

Temperature-Dependent Positron Trapping in Copper and Aluminum Tubes after Tensile Deformation. T.Wider, K.Maier, U.Holzwarth: Physical Review B, 1999, 60[1], 179-90