An in-situ field ion microscope study of irradiated tungsten II. Analysis and interpretation

In Part I (see previous paper) the results of a series of experiments demonstrated that self-interstitial atoms (SIAs) were immobile at an irradiation temperature of 15°k, and that these same SIAs subsequently underwent long-range migration at temperatures as low as ~28°k. In this paper we analyse these results quantitatively, and obtain approximate values of the diffusion coefficient [≃0·22 exp (–0·085 ev/kT) cm² sec^–1], and the enthalpy change of migration of the SIA (~ 0·085 ev). The effect of the electric field on the diffusivity of a single SIA was considered, and it was shown that the volume change of migration for a SIA must have been 2 ≲ 0·1 atomic volume. The problems of SIA clustering and the formation of SIA-impurity atom clusters were considered and were shown to be possible sources of the broad annealing spectrum reported in Part I. In addition the relationship of the post-anneal field evaporation experiments to the 2-interstitial recovery model was discussed. Finally, the present experiments were compared with other Stage I recovery data on irradiated tungsten.