Direct determination of long-range dipolar interactions in Kr by neutron diffraction

Neutron diffraction experiments at low momentum transfer q offer the remark able possibility to simultaneously measure the strength of the longest-rang e two- and three-body interactions in classical fluids, namely the London d ouble-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 a nd liquid Kr show that, by investigating a wide density range, a direct, i. e. model-independent, experimental determination of long-range forces can b e performed.