Thermal neutron scattering properties of Bismuth crystal filter

Accurate thermal neutron scattering cross-section data of the Bismuth (Bi) filter is required for high-fidelity calculations of the thermal neutron beam’s performance after the filtration in reactor column. In this paper, the phonon density of states of Bi was calculated using the ab initio method, based on which the thermal neutron scattering cross-section data was generated by the introduction of Bi coherent scattering model. By comparing the numerical results with the experimental data, the applicability of the model is verified. The model is then applied to simulate the neutron beam-shaping effect in the filter with an incident neutron spectrum in a research reactor column. Compared with the free gas model, the thermal neutron fraction was enhanced remarkably with an accurate phonon spectrum, and the phenomenon of Bi neutron filtration can be captured.