CALCULATIONS OF POSITRON LIFETIMES IN A JOG AND VACANCIES ON AN EDGE-DISLOCATION LINE IN FE

The lifetimes of positrons in an edge dislocation, a jog, and vacancies, which are associated with the edge dislocation (associated vacancy), in bcc iron are calculated. The structures of the defects are obtained by static relaxation using the Finnis-Sinclair potential. The positron lifetimes are calculated using the superimposed-atom method, which was developed by Push and Nieminen. The positrons are not localized strongly in the pure edge dislocation and the jog. The lifetimes in them are almost the same, and are only a few picoseconds longer than in the matrix. The vacancy is trapped on the edge-dislocation line, and is not collapsed completely by the strain in the core region of the dislocation. The positron lifetime in the associated vacancy is shorter than that in a vacancy in the matrix, and is compared to the experimental value observed in deformed iron. These results indicate that the deeper trap associated with the dislocation line is not the jog but the vacancy.