Evidence that helium irradiation blisters contain high-pressure gas

Trapping of ∼20-keV helium in Be, Cu, and Nb at fluences near the blistering threshold has been investigated by proton backscattering and by elastic recoil detection. Blister cavities at a depth close to the mean range contain up to 2.3×1017 He/cm2 (or more), corresponding to pressures in kbars, in agreement with gas pressure models. Depending on the metal, and its condition (annealing, stresses), the blisters may or may not rupture and release a large burst of helium. The re-emission data of Bauer et al. agrees qualitatively with these trapping data.