MEASUREMENT OF THE KINETIC-ENERGY IN HE-4 THROUGH THE SUPERFLUID TRANSITION BY VERY-HIGH-ENERGY NEUTRON-SCATTERING

Measurements of the kinetic energy of atoms in liquid He-4 have been m ade using neutron Compton scattering at wavevector transfers between 9 0 and 150 Angstrom(-1). The kinetic energy shows a marked decrease fro m 16.2 K at a temperature of 2.5 K, to 13.9 K at 1.3 K. Three differen t measurements were made using energy analysers with different resolut ions. Good agreement was obtained between the measurements using diffe rent resolutions and with previous measurements and calculations of th e kinetic energies. For the best-resolution data, a line shape analysi s was made in order to derive the non-Gaussian components of the momen tum distribution. Values of kinetic energies are consistent with a Bos e condensate fraction of similar to 10%. The measurements show that eV neutron scattering provides an accurate method of measuring kinetic e nergies in quantum fluids.