Momentum Density of hcp ${}_{}{}^4{}_{}{}^{}\mathrm{He}$

The momentum density of the quantum solid hcp ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ has been measured at 1.70 K at the molar volumes 18.20 and 19.45 ${\mathrm{cm}}^3$. The measurements were made with pulsed incident neutrons of energy 505 meV, and with momentum transfers in the range of 12 to 22.5 ${\mathrm{\AA }}^{-1\mathrm{}}$. The momentum density is obtained from the inelastic-scattering spectrum at each of eight scattering angles. The measured distribution is Gaussian and the derived kinetic energies are larger than proposed by existing theories.