Thermal desorption of tritium and helium in aged titanium tritide films

Abstract

Titanium films were deposited onto molybdenum substrates and then converted into titanium tritides (TiT1.5–1.8) films inside a tritiding apparatus loaded with pure tritium gas. Evolution of tritium and helium in the titanium tritide films over a period of four years was investigated using a thermal desorption technique, together with X-ray diffraction analysis. Results showed that desorption profiles of the tritium varied significantly with the evolution of He contents. Apart from the primary peak from tritium desorption located at a temperature between 610 and 840 K, another higher temperature tritium desorption peak (at ∼950 K) was observed, attributed to damages in the lattice structures induced by generation of 3He bubbles. Release of helium in the tritide film became significant after a long term aging process (i.e., after a few years). Depending on the amount of the 3He bubbles generated due to the decay of tritium, spectra of the thermal helium desorption showed five peaks in the range from room temperature to ∼1750 K, corresponding to different states of helium evolution during aging of the titanium tritide films. The amounts of helium desorption in different stages were estimated, and the dissociation energy of helium from different trap states as a function of the aging duration was obtained.