( n,2 n) and ( n,3 n) cross-sections of neutron-induced reactions on 150Sm for [formula omitted] MeV

Abstract

Cross-section measurements were made of prompt discrete γ -ray production as a function of incident neutron energy ( E n = 1 – 135 MeV ) on a 150Sm sample of 1550 mg / cm 2 of Sm 2 O 3 enriched to 95.6% in 150Sm. Results are compared with enhanced Hauser–Feshbach model calculations including the pre-equilibrium reactions. Energetic neutrons were delivered by the Los Alamos Neutron Science Center facility. The prompt-reaction γ -rays were detected with the compton-suppressed germanium array for neutron-induced excitations (GEANIE). Incident neutron energies were determined by the time-of-flight technique. Excitation functions for thirteen individual γ -rays up to E x = 0.8 MeV in 149Sm and one γ -ray transition between the first excited and ground state in 148Sm were measured. Partial γ -ray cross-sections were calculated using GNASH, an enhanced Hauser–Feshbach statistical nuclear reaction model code, and compared with the experimental results. The particle transmission coefficients were calculated with new systematic “global” optical model potential parameters. A coupled-channels optical model based on a soft rotor model was employed to calculate the particle transmission coefficients. The pre-equilibrium part of the spin-distribution in 150Sm was calculated using the quantum mechanical theory of Feshbach, Kerman, and Koonin (FKK) and incorporated into the GNASH reaction model code. The partial cross-sections for discrete γ -ray cascade paths leading to the ground state in 149Sm and 148Sm have been summed (without double counting) to estimate lower limits for reaction cross-sections. These lower limits are combined with Hauser–Feshbach model calculations to deduce the reaction channel cross-sections. These reaction channel cross-sections agree with previously measured experimental and ENDF/B-VII evaluations.