Cold-Neutron Scattering Cross Section of Liquid Hydrogen Based on a Consistentvibrations Liquid Model

摘要

Expressions for the elastic and inelastic slow-neutron cross sections of liquid hydrogen are derived, with liquid effects accounted for on the basis of a harmonic oscillator model. It is assumed that the molecules can be regarded as rigid rotators, the centers of mass of which execute quantized harmonic motions about central sites in a liquid quasi-lattice. A consistent-vibrations liquid model presented in AD-614 039, provides the statedependent vibration parameters and the neighbor distributions resulting from thermal disorder. The derived cross sections may be divided into diffuse and interference parts. Insofar as the molecular motion conforms to a system of independent oscillators, the inelastic scattering, which may result from rotational molecular excitation, from excitation of a quantum level of the center-of-mass motion, or from both processes simultaneously, is purely incoherent. The interference scattering is found to be independent of the relative concentrations of para- and orthohydrogen. Calculated para-hydrogen cross sections for various inelastic processes associated with the scattering of 0.065-ev neutrons through 90 degrees are compared with a published experimental spectrum. (Author)