Small-angle scattering of neutrons on large scale inhomogeneities in   refraction range
  The small-angle scattering of neutrons on large scale inhomogeneities of two-component systems in refraction range is considered. We supposed, that neutrons acquire phase shifts describing by the Gaussian distribution function. It is shown that the average cross section of scattering contains two contributions. The first contribution describes the diffraction and in the asymptotic limit of large transfer momentum this contribution is proportional to q^{- \Delta}, where 2 \leq \Delta \leq 4. The second contribution is similar to the Fraunhofer diffraction, which in the asymptotic limit of large transfer momentum is proportional to q^{-3}. 
Y. N. Skryabin and A. V. Chukin