Helium diffusion in metals investigated by nuclear reaction analysis

Abstract The 3 He(d,p) 4 He resonance reaction provides a mean to monitor helium depth profiles in solids, in particular by scanning the d-energy and detecting the emitted ∼13 MeV protons, easily discriminated from other reaction by-products. In the present work, we followed the change, induced by isothermal annealing, in the depth profile of helium-3 implanted in a Au–Ag alloy. Results show that helium profiles are only affected by high temperature and large annealing time and depart from a Gaussian distribution, i.e. the diffusion does not follow Fick’s law. Results also indicate that one part of the helium diffuses towards the surface while the other remains trapped at the implantation depth. The asymmetrical profile enhancement evidenced on its upstream side is either due to intermediate trapping by radiation induced defects or due to a diffusion enhancement in the vicinity of a surface acting as a non-saturated “trapping site”.