The three-body interaction in fluids studied by SANS

Diffraction measurements can provide the only direct experimental access to the long-range features of the pair and triplet interaction potentials of monatomic fluids. This is done by measuring the low-q behaviour of the static structure factor S(q) which is related to the asymptotic parts of the interaction. Recently we have performed several neutron experiments in rare gas fluids, at various temperatures and pressures, in order to study the two- and three-body dispersion forces. Here we shall report and discuss the results of low-q measurements on Kr and Xe in various thermodynamic conditions.