Gas densities in he bubbles and their size distribution in nickel measured by neutron scattering

Abstract

The density of helium in bubbles produced in two Ni isotopes by α-implantation and isochronal annealing has been measured by the contrast variation method of SANS. A further evaluation of the SANS data after the last annealing step at 1123 K yielded a bimodal size distribution. Assuming equilibrium bubbles a consistent set of parameters characterizing the bubble populations could be extracted from the scattering data. Those parameters for the “small” and “large” bubbles are: The atomic He densities are 0.7 and 0.17 of the atomic Ni density, the mean radii are 1.2 and 13 nm, the volume fractions are 0.011 and 0.0074 and the He contents are 790 appm and 120 appm, respectively. The values for the “small” bubbles are in good agreement with the TEM results. However, the existence of “large” bubbles could not be confirmed by TEM, probably because of a spatially inhomogeneous distribution.