Abstract
Neutron diffraction experiments at low momentum transfer q offer the remarkable possibility to simultaneously measure the strength of the longest-range two- and three-body interactions in classical fluids, namely the London double-dipole and the Axilrod-Teller triple-dipole potentials, without need to resort to any model for the pair interaction. The results here reported of a new neutron diffraction study on the low-q structure of both gaseous and liquid Kr show that, by investigating a wide density range, a direct, i.e. model-independent, experimental determination of long-range forces can be performed.