Neutron scattering cross sections of cryogenic moderator materials. Some results from the Synthetic Model

The Synthetic Scattering Function (SSF) allows a simple description of the incoherent interaction of slow neutrons with hydrogenous materials. Its original formulation, essentially aimed at describing molecular gases, has been extended to include the important case of molecular solids. In any case, the main advantages of the Synthetic Model reside in the analytical expressions that it produces for double-differential cross sections and energy-transfer kernels, which in turn permit the fast evaluation of neutron scattering and transport properties. The SSF routines were integrated into the NJOY code, in such a way that the cross sections can be generated with the same format either from its standard library or from our model. We discuss in this work some aspects of the formalism developed to include the case of molecular solids in a more detailed manner, and present applications of the original and extended Synthetic Model to recent experimental results on liquid Hydrogen, Mesitylene, and solid Methane. (author)