Low-q structure of Kr gas at undercritical densities: an accurate SANS determination of triplet forces

The low-q part (1<=q/nm-1<=5.5) of the structure factor S(q) of Kr has been measured at five densities below 4.3 nm-3 by means of neutron diffraction. The three-body interaction contributions to the low-q structure are reliably extracted from the density dependence of the data, leading to the best experimental determination of the Axilrod-Teller forces in a rare-gas fluid.