Evolution of the lattice spacing and damage in tantalum tritide

The evolution of the lattice spacing and damage of tritium-charged tantalum during aging is studied by x-ray diffraction. The lattice spacing is found to increase only very weakly with the atomic helium concentration $c_{\mathrm{He}}$ built up upon tritium decay, while the lattice damage monitored by peak broadening increases significantly. With the combination of the lattice-parameter measurements with recent dilatometric measurements it is concluded that already at very low $c_{\mathrm{He}}\gtrsim 2\times {10}^{-4\mathrm{}}$ tantalum self-interstitials generated in association with helium bubble formation induce an evolution of a dislocation network. This conclusion is shown to be consistent with the observed peak broadening.