Neutron Cross Sections Libraries for Methane in Phase II and Solid Deuterium

Abstract

Centro Atomico Bariloche, Argentina andCONICET, Argentina(Received 26 April 2010)We present new cross section libraries for two materials of interest as very cold and ultra coldneutron moderators: solid Methane in phase II and solid Deuterium. A simple model to describe theinteraction of slow neutrons with solid methane in phase II (T <20.4 K) was developed, includingthe main dynamical features of the system and the e ect of spin correlations. Its predictionsare in good agreement with a quantum mechanical calculation over the limited range where thelatter was formulated, and with available experimental information over the complete thermalenergy range. Also, we introduce cross section libraries based on a new scattering kernel recentlydeveloped to describe the interaction of slow neutrons with solid Deuterium (T <18.7 K). The maincharacteristics of that system are contained in the model, including the lattice’s density of states,the Young-Koppel quantum treatment of the rotations, and the internal molecular vibrations. Theelastic processes involving coherent and incoherent contributions are fully described, as well as thespin-correlation e ects. The results from the new model are compared with the best availableexperimental data, showing very good agreement.