Differential cross section for neutron scattering from Bi209 at 37 MeV and the weak particle-core coupling

Differential scattering cross-section data have been measured at 43 angles from 11^° to 160^° for 37-MeV neutrons incident on Bi209. The primary motivation for the measurements is to address the scarcity of neutron scattering data above 30 MeV and to improve the accuracy of optical-model predictions at medium neutron energies. The high-statistics measurements were conducted at the China Institute of Atomic Energy using the H3(d,n)He4 reaction as the neutron source, a pulsed deuteron beam, and time-of-flight (TOF) techniques. Within the resolution of the TOF spectrometer, the measurements included inelastic scattering components. The sum of elastic and inelastic scattering cross sections was computed in joint optical-model and distorted-wave Born approximation calculations under the assumption of the weak particle-core coupling. The results challenge predictions from well-established spherical optical potentials. Good agreement between data and calculations is achieved at 37 MeV provided that the balance between surface and volume absorption in a recent successful model is modified, thus suggesting the need for global optical-model improvements at medium neutron energies.