Density evolution of the kinetic energy of fluid and solid He-4 at T=6.1 K

By means of neutron Compton scattering, we have measured the momentum distribution of He-4, on the isotherm T = 6.1 K, in the pressure range between 0 and 500 bars. The second moment of the distribution gives the value of the kinetic energy. This is a function of density that increases from the classical value (3/2)k(B)T up to similar to 5 times this value in the compressed solid. The kinetic energy data show a change in the density behavior at melting. This suggests that the change of symmetry influences the single-particle distribution function.