The thermal release of helium injected into nickel, stainless steels and nimonic PE16

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Abstract
The release of helium from nickel, 316 and 18/8 stainless steels and nimonic PE16 foils uniformly filled with helium to concentrations of the order of 10−5 atom/atom has been measured during linear rise anneals and compared with the release from nickel foils implanted with low energy helium ions. Annealing peaks have been observed and attributed to radiation damage annealing, helium diffusion to form gas bubble nuclei, and gas release by bubble migration. The fraction of helium released has been found to be concentration dependent and to be much smaller from stainless steels than from nickel. This is attributed to increased trapping. The activation energy for diffusion of helium in nickel was found to be ∼ 2.50 eV. In nickel annealed at 600°C all of the helium is incorporated in bubbles, which are predicted to be approximately 20 Å, diameter. It is concluded that voids formed by ion bombardment to high doses at elevated temperatures in helium filled foils are nucleated on these bubbles.