Isotope Effects and Helium Retention Behavior in Vanadium Tritide

The relaxation times of the H, T, and ³He nuclei have been measured in vanadium hydride and tritide samples. Substantial isotope effects in both the phase transition temperatures and diffusion parameters have been found. When compared to hydrides, the tritide samples have lower transition temperatures and faster mobilities. The differences in the occupancies of the interstitial sites are largely responsible for these isotope effects. Most of the helium atoms generated by tritium decay remain trapped in microscopic bubbles formed within the VT_x lattice. Evidence is presented for the gradual growth of the helium bubbles over periods of hundreds of days.