The influence of irradiation, with sub-threshold energy, upon vacancy diffusion (not usually considered in radiation effects), was investigated. The displacement threshold energy, Ed, was investigated in tungsten. It depended strongly upon orientation and the minimum Ed value was 68eV for the <100> direction. The recoil energies for vacancy migration also depended strongly upon the orientation, and were equal to 1.9, 9.4 and 52.9eV for the <111>, <100> and <110> directions, respectively. The average recoil energy for vacancy migration was estimated to be 3.1eV. This implied that vacancy diffusion was enhanced by irradiation even in the low-energy range below the displacement threshold energy. In addition, the recoil atom interacted not only with the nearest-neighbor vacancies, but also with distant vacancies. The long-distance interaction between the recoil atom and a vacancy was prominent in the <111> direction.

Molecular Dynamics Simulation of Vacancy Diffusion in Tungsten Induced by Irradiation. Xu, Q., Yoshiie, T., Huang, H.C.: Nuclear Instruments and Methods in Physics Research B, 2003, 206, 123-6Table 19

Diffusion parameters for Zn4Sb3