Pure Ni, and alloys which contained 1 or 3at%Sb, were implanted with 25keV He+ ions at 600 and 700C. It was found that the addition of Sb significantly increased the densities of loops and cavities in the presence of implanted He atoms. The density ratio of loops and cavities was equal to 0.1 at 600C and to 0.006 at 700C. It was concluded that the nucleation of loops and cavities was controlled by the same factor. Other studies showed that the trapping of vacancies by Sb atoms was very strong, and it was suggested that Sb-He-vacancy clusters could be the nucleation sites. Loops would be nucleated only by the smallest clusters, while larger clusters (cavities) would act as sinks for point defects. The marked reduction in the loop/cavity density ratio, between 700 and 600C, was attributed to the disappearance of small Sb-He-vacancy clusters by absorption into larger clusters or by escape to the surface before they could act as nucleation sites for loops.

K.Niwase, T.Ezawa, T.Tanabe: Journal of Nuclear Materials, 1994, 212-215[A], 364-9