Helium bubble growth in nickel at temperatures below vacancy migration

It is shown that bubble growth in nickel during 5 keV He+-implantation in the temperature range 200 K-600 K and dose range 5x1020 He+/m2-1022 He+/m2 can fairly well be described by a loop-punching mechanism. The results indicate that not all helium that remains in the matrix has precipitated into visible bubbles. With increasing dose, however, the percentage of helium in the bubbles increases. It is also shown that at 2x1021 He+/m2 the helium bubble distribution changes from a random distribution to a partially ordered distribution. The bubbles are ordered in some planes of the fcc nickel matrix, but ordering is lacking in other planes. (orig.)