X-ray scattering from liquid He3-He4 mixtures

Structure factor of liquid He mixtures of He3 concentration x =0.11, 0.20, 0.24, 0.26, 0.31, 0.35, and 0.40 at T=1.7 K have been obtained experimentally by x-ray scattering. The structure factor shows a lowering of the peak height and a shift to smaller momenta in its position for the increasing He3 concentration. Furthermore, it presents some fixed points of scattering momentum at which the values of the structure factors are not influenced by the variation of He3 concentration. In order to aid the understanding of the origin of these fixed points, a simple model which is an extension of the Bogoliubov theory to the mixture has been constructed. The structure factor calculated on this model shows a good agreement with the experiment. The fixed points in the model turn out to be at interaction-free momenta.