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Abstract
Positron annihilation studies have been carried out in austenitic stainless steel (SS 316), irradiated with high energy helium and deuteron ions from a cyclotron. Defect states have been deduced from simultaneous measurements of positron lifetime and Doppler lineshape in post-irradiation anneal up to 1473°K. Clear differences in the annealing characteristics are observed beyond 673°K between the helium- and deuteron-irradiated specimens. Evidence is presented for helium-vacancy interaction and nucleation of helium bubbles. Results on helium in nickel are also discussed for comparison. Helium agglomeration to microbubbles, which are well below the resolution of electron microscopy, is detected around 800°K. In the growth stage of bubbles at higher temperatures, two distinct positron bound states develop both in SS 316 and nickel. Helium retention in large bubbles is found to be stable even at 1473°K in SS 316.