Thermal neutron scattering cross sections of beryllium and magnesium oxides

•Neutron thermalization in BeO and MgO was studied using Ab initio lattice dynamics.•The BeO phonon density of states used to generate the current ENDF library has issues.•The BeO cross sections can provide a more accurate ENDF library than the current one.•For MgO an ENDF library is lacking: a new accurate one can be built from our results.•BeO is a better filter than MgO, especially when cooled down to 77K. Alkaline-earth beryllium and magnesium oxides are fundamental materials in nuclear industry and thermal neutron scattering applications. The calculation of the thermal neutron scattering cross sections requires a detailed knowledge of the lattice dynamics of the scattering medium. The vibrational properties of BeO and MgO are studied using first-principles calculations within the frame work of the density functional perturbation theory. Excellent agreement between the calculated phonon dispersion relations and the experimental data have been obtained. The phonon densities of states are utilized to calculate the scattering laws using the incoherent approximation. For BeO, there are concerns about the accuracy of the phonon density of states used to generate the current ENDF/B-VII.1 libraries. These concerns are identified, and their influences on the scattering law and inelastic scattering cross section are analyzed. For MgO, no up to date thermal neutron scattering cross section ENDF library is available, and our results represent a potential one for use in different applications. Moreover, the BeO and MgO efficiencies as neutron filters at different temperatures are investigated. BeO is found to be a better filter than MgO, especially when cooled down, and cooling MgO below 77K does not significantly improve the filter’s efficiency.