The influence of irradiation with sub-threshold energies upon vacancy diffusion, which was not usually considered in radiation effects, was investigated by means of molecular dynamics simulations. The displacement threshold energy, E, was investigated in W. It depended strongly upon orientation, and the minimum E-value was 68eV in the <100> direction. The recoil energies for vacancy migration also depended strongly upon the orientation, and were 1.9, 9.4 and 52.9eV in 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 which was less than the displacement threshold energy. In addition, the recoil atom interacted with not only the nearest-neighbor vacancies, but also with distant vacancies. Long-range 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. Q.Xu, T.Yoshiie, H.C.Huang: Nuclear Instruments and Methods in Physics Research B, 2003, 206, 123-6