Long range potential effects in low density krypton gas

Small angle neutron scattering (SANS) in low density Kr-86 gas has been performed in order to measure the small-k behavior of the static structure factor S(k). Three number densities between 1.52 and 2.42 nm(-3) along the T = 297 K isotherm have been studied. The small-k dependence of the Fourier transform c(k) of the direct correlation function c(r) has been derived. The experimental determination of the k(3) term in the behavior of c(k) has led to a direct measurement of the London dispersion interaction in the pair potential of krypton. Also the contribution of the three-body potential in the asymptotic behavior of c(r) has been observed and related to the magnitude of the three-body interaction potential.