The wave like pattern, observed in dislocation dipoles of uniform spacing during annealing, which starts from the ends of the dipole and gets damped toward the centre, has been attributed to controlled vacancy migration. A theory has been set-up to give activation energy for the process, 60,700 + 2,000 cal/mole. This value has been compared with an independent study of pipe diffusion, in which a prismatic loop inside the foil is connect to both surfaces of the foil by screw dislocation.