Neutron scattering and atomic dynamics in liquid nickel

Abstract

The results of inelastic neutron scattering experiments on liquid nickel at a temperature of 1870°K are reported, one set of measurements being performed on natural and another on an incoherently scattering mixture of nickel-58 and nickel-62 isotopes. From these data the dynamic structure factor S(q, ω) and the self function S_s (q ω) have extracted over a limited range of q (2.2 < q < 4.4 A⁻¹) and ω (0 < ω < 80 meV). To interpret S_s (q, ω) a model is used which attempts, as is usual, a precise description of the short-time behaviour of the atomic motions. The theory is characterized by two quantities for which first principles expressions are available. Because of uncertainities in (a) the interionic potential and (b) the static triplet correlation function, these two quantities are treated as parameters in the model. The main features of the incoherent scattering data are reflected by the model. The coherent scattering data provides some preliminary evidence for the existence of collective modes in liquid nickel. Such modes, if they exist, would have to be due, at least in part, to the long-range force in the pair interaction, which has been estimated previously from the static structure factor S(q). Finally, approximations to S(q, ω) are calculated from the observed values of S(q), using both measured data, and the model, for S _s and the usefulness and limitations of such relations are briefly assessed.