MICROSCOPIC APPROACH TO THE RESPONSE OF HE-3-HE-4 MIXTURES

Correlated-basis-function perturbation theory is used to evaluate the zero-temperature response S(q,omega) of He-3-He-4 mixtures for inelast ic neutron scattering, at momentum transfers q ranging from 1.1 to 1.8 Angstrom(-1). We adopt a Jastrow correlated ground state and a basis of correlated particle-hole and phonon states. We insert correlated on e-particle-one-hole and one- and two-phonon states to compute the seco nd-order response. The decay of the one-phonon states into two-phonon states is accounted for in the boson-boson approximation. The full res ponse is split into three partial components S,p(q,omega), each of the m showing a particle-hole bump and a one phonon, delta-shaped peak, wh ich stays separated from the multiphonon background. The cross term S, (q,omega) results to be of comparable importance to S-33(q,omega) in t he particle-hole sector and to S-44(q,omega) in the phonon one. Once t he response has been convoluted with the experimental broadening, the computed scattering function is in semiquantitative agreement with rec ent experimental measurements.