On the Theory of Coherent Scattering Processes in Liquids

Abstract

The coherent scattering structure factor of liquids for x-rays and slow neutrons are shown to determine completely both the correlation function and the direct local interaction function of liquids, which quantities are the only operating elements of the general static liquid model of Ornstein and Zernike. Of these functions only the former has been derived so far from the data accumulated essentially on the coherent scattering of x-rays by liquids. It is shown that the directly available experimental structure factors completely determine the even moments of these molecular distribution functions. The zeroth moment of the correlation function augmented by unity is essentially the liquid concentration fluctuation which determines its isothermal compressibility. These quantities become thus directly derivable from the structure factor measurements without any arbitrary and uncertain manipulations In terms of the model, a straightforward method leads, with the empirically obtainable total cross section, to the total incoherent slow neutron scattering cross sections in liquids. These should yield information on their energy spectrum not available through other types of scattering processes, such as x-rays, for instance.