Studies on reflector materials for cold neutrons

In this work we present calculations aimed at evaluating the thermal neutron cross sections of bulk diamond and the small angle scattering contribution due to the nano-structure, using recent experimental information. With those ingredients we generated a cross section library over an extended neutron energy range for a real nano-diamond (ND) powder. Reflectivity calculations using our library confirm the excellent performance of that material for ultra-cold and very cold neutrons, and also its rapid decrease for neutron velocities larger than about 150 m/s. A different approach was employed to explore the characteristics of potential cold neutron reflectors, based on the requirement of a large scattering cross section combined with a small value of the average cosine of the scattering angle over the energy range of interest. Those conditions led us to consider metal hydrides, and eventually select magnesium hydride (MgH₂) as a good candidate to fulfill those requirements