C.T. Chudley

The incoherent inelastic scattering cross section of slow neutrons from liquids is calculated using a simple model in which the liquid is assumed to have appreciable short range order in a quasi-crystalline form. Diffusive motion takes place in large discrete jumps, between which the atoms oscillate as in a solid. The model predicts a definite, easily calculable cross section which is not dominated by diffusion effects as when continuous diffusion is assumed, but shows a characteristic variation with angle which could be looked for experimentally. The related pair correlation functions are dominated at small r and t by vibrational effects. Although simple and extreme the model explains several aspects of the observations of Brockhouse and Pope in 1959 and others. A brief discussion of the coherent scattering cross sections for the model is given although explicit formulae are not obtained.

rons by light and heavy water for use in reactor calculations is considered. The main criterion used for the models is that they should be in good agreement with measurements of the neutron diffusion coefficient, and an extensive review is given of experimental diffusion data for both light and heavy water. Various simple models are presented and compared with experimental measurements of diffusion parameters, total cross-section and, for light water only, the mean kinetic energy of the hydrogen atom. (auth)