The results of neutron scattering experiments with scattering vectors $0.06\le Q\le 0.14$ ${\mathrm{\AA }}^{-1\mathrm{}}$ and $0.27\le Q\le 1.50$ ${\mathrm{\AA }}^{-1\mathrm{}}$ are discussed in terms of hydrodynamics. It is found that the small-$Q$ data, at low densities, exhibit a distinct Brillouin triplet, describable by hydrodynamic theory. At larger $Q$, and at higher density, a hydrodynamic description is still possible with simple $Q$ and $\omega$ dependences of the transport coefficents, namely a heat diffusion $D_T=D_T^0{(1+Q^2{r}_0^2)}^{-1\mathrm{}}$ and a viscosity $\phi ={\phi }^0{\tau }_0^{-1\mathrm{}}{[-i\omega +{\tau }^{-1\mathrm{}}\mathrm{}(Q\left)\right]}^{-1\mathrm{}}$ with $\tau \mathrm{}\left(Q\right)={\tau }_0{(1+Q^2{R}_0^2)}^{-1\mathrm{}}$. The relaxation lengths and times for the establishment of local equilibrium are found to be on the order of a few Angstroms and ${10}^{-13\mathrm{}}$ sec, respectively.

• Received 8 July 1974

DOI:https://doi.org/10.1103/PhysRevA.11.316