Measurement of acoustic phonons inUBe13

The low-energy phonon dispersion of ${\mathrm{UBe}}_{13}$ has been measured by means of inelastic neutron scattering at room temperature and 10 K and elastic constants have been extracted. They are consistent with values obtained by scaling from pure beryllium, and the angular variation is almost isotropic. The lattice contribution to the low-temperature specific heat has been calculated from these data and is compared with the measured specific heats in the literature.