The two-body collision term in the density expansion of the dynamical structure factor of argon determined by neutron scattering

The dynamical structure factor of Ar gas at room temperature and at various low densities is measured as an extension and improvement of earlier measurements by means of small angle inelastic neutron scattering. The linear term in the density expansion of the dynamical structure factor is determined and compared with Boltzmann theory. It is found that the hard sphere theory and the data agree only qualitatively.