Dynamics of hydrogen in Ta in the mK-region

The low-temperature diffusion of hydrogen and deuterium in Ta was investigated using the method of perturbed angular correlation. In an ealier paper we reported the results of measurements above 4 K. These experiments have now been extended down to 10 mK. We found that the configuration of trapped hydrogen and deuterium changes, if the sample is cooled from 4.2 K to 10 mK. We suggest that this change is due to a transition of an extended to a more localized wave function of H (D).