Dynamical Quadrupole Interactions in the Hafnium Deuterium System

Abstract

The nuclear quadrupole interaction (NQI) at the site of 181Ta in HfD2 has been investigated by time differential perturbed angular correlation measurements. Below 290 K the NQI is static within a 300 nanosecond time window. Above 290 K dynamic effects related to the diffusion of deuterium atoms start to appear, which have been analyzed in terms of a 3-state stochastic model. Between 345 K and 500 K the jump diffusion of deuterium has an activation energy Ea = (0 .3 3-0.4 +0.9 ) eV. At higher temperatures the relaxation spectra suggest that transitions occur, first to the δ-phase, then to the α-phase of the hafnium-deuterium system. At 600 K the mean residence time between jumps is of the order of 2 nanoseconds. First measurements with HfH2 show an isotope effect compatible with the prediction of the classical rate theory for over-barrier diffusion.