Positron Trapping at Dislocations in Copper

Abstract

Measurements of positron lifetimes in cold worked copper samples show clearly positron trapping by dislocations. The copper crystals were deformed under conditions that would lead to known densities of dislocations in near random arrays and were annealed to remove other defects associated with the deformation. Using a trapping model, the data yields the value of μ = 2.9 × 10 15 s −1 for the trapping rate per unit defect concentration, somewhat higher than the rate for trapping by vacancies in copper. The increase in lifetime of positrons trapped at dislocations is 34 ps (26%), about half the change for positrons trapped at vacancies in copper. A discussion of positron trapping at dislocations contrasted to vacancies emphasizes the differences arising from the extended nature of the dislocation. The theoretical picture leads to a trapping rate at dislocations roughly proportional to the binding energy.