Low Energy Neutron Interactions with Uranium Carbide

The double-differential scattering cross section of polycrystalline natural uranium carbide (UC) has been measured for incident energies of 0.092, 0.135, and 0.159 eV. Inelastic scattering peaks corresponding to excitation energies of 0.013 and 0.045 eV were observed and are shown to belong to acoustic and optical modes of the UC lattice. A model has been developed using a normal mode analysis based on the Born and Von Kármán approximation, including noncentral forces and considering up to third-nearest neighbors. A theoretical scattering law has been derived based on this analysis. Resolution and multiple scattering effects have been calculated using a new Monte Carlo approach. After the application of these corrections, the double differential cross sections derived from the theoretical scattering law agree with the measurements. The variation of the specific heat with temperature is accurately predicted by the model. The total cross section was also measured for the energy range 0.006 to 3.5 eV. The Bragg peaks due to coherent scattering were resolved up to 0.05 eV. The total cross section calculated from our noncentral force model compares well with this measurement.