Two plateaux for palladium hydride and the effect of helium from tritium decay on the desorption plateau pressure for palladium tritide

Two plateaux are observed in the desorption isotherm for palladium hydride: a lower plateau pressure for a hydrogen/metal atom ratio (H/M) less than about 0.3 and a slightly higher plateau pressure for H/M greater than about 0.3. This higher pressure corresponds to the reported pressure for palladium hydride. These observations were made for a large surface area palladium powder exposed to both protium and tritium. Helium buildup from tritium decay decreases the lower plateau pressure but does not affect the observations for H/M greater than about 0.3. A multiple-energy hydrogen site occupancy model is proposed to explain qualitatively both the dual plateau and the helium effect in palladium hydride.