A study of tracer and collective diffusional processes in α'-NbD0.7at 600 K using quasielastic neutron scattering with spin analysis

The authors have used neutron polarisation analysis to measure, separately, the self and collective dynamics of a high-concentration lattice gas of deuterium in a single crystal of niobium. The measured incoherent scattering has been found to be well described by the dynamical model due to Rowe et al (1971), and the coherent scattering function is adequately described by a simple adaptation of this model, in which the quasielastic line width narrows with increases in the structure factor, S(Q). Estimates of the diffusion coefficients and correlation factors appropriate to tracer and collective processes, together with the thermodynamic factor, have been determined from model fitting. Information on the interstitial ordering and the extent of the interactions has also been deduced and is in accordance with current Monte-Carlo predictions (Faux and Ross 1987) within the bounds of the expected site blocking and availability. They believe this experiment to be the first to employ the polarisation analysis technique to study tracer and collective diffusion.