Observations on ³He Release from ERT₂ Films

We have hydrided thin (500 nm) films of Er with tritium to a stoichiometry of ErT₂, and have been observing their ³He release characteristics at very low ³He/Er ratios. The films are stored in vacuum-tight metal containers and sampled on a timescale ranging from a day to several months. Analysis is performed with very high sensitivity using static noble gas mass spectrometry. For the first several years, ³He release is a fairly constant function of helium generation, and does not depend on the amount of helium accumulated in the film. There appears to be somewhat higher helium release at very early times (up to 2%), decreasing over 6 months to a fairly flat value (0.7%). This observation is consistent with a bubble nucleation and growth mechanism. The very early release behavior does not appear to be dependent upon the presence or growth of surface oxide layers.