FIRST OBSERVATION OF INELASTIC X-RAY-SCATTERING FROM CONDENSED HE-4 USING HIGH-ENERGY RESOLUTION

Recently, the suitability of inelastic X-ray scattering for the invest igation of solid and fluid He-4 has been demonstrated. For the test ex periments an energy resolution of the order of 10-15 meV was used at t he backscattering spectrometer INELAX at the storage ring DORIS of DES Y, Hamburg. Lattice excitations were observed for momentum transfers a long the c axis of h.c.p. helium crystals which were grown in situ at pressures of 54-63 MPa and at temperatures of 4.2-6.4 K. At 10 K above the melting point, energy-loss signals could also be detected from th e liquid helium at equivalent momentum transfers.