Hydrogen trapping at hafnium and hydrogen diffusion in tantalum

Trapping of hydrogen and deuterium at the substitutional impurity hafnium in tantalum was studied by the perturbed angular correlation (PAC) technique with the radioactive probe 181Hf/181Ta. Two different hydrogen configurations could be distinguished which were assigned to a single H(D) and to several H(D) atoms trapped at Hf, respectively. The quadrupole interactions caused by H and D at the probe site are the same within the experimental errors. In an annealing experiment it was found that the Hf-H and Hf-D complexes vanish around 55 K and 62 K, respectively. In addition, the diffusion coefficients of H in Ta were measured at low temperatures. They are several orders of magnitude larger than expected from the extrapolation of the known data with an Arrhenius function. (orig.)