The low-Q part (0.47 < Q (nm(-1)) < 4.15) of the static structure factor S(
Q) of Kr-86 has been derived at five low densities and room temperature by
a small-angle neutron diffraction measurement and a careful treatment of ex
perimental corrections. From the data the small-Q dependence of the Fourier
transform c (Q) of the direct correlation function c (r) has been obtained
and has allowed the first accurate experimental determination of the long-
range three-body Axilrod-Teller potential strength in a classical fluid.