Differential cross section for neutron scattering fromBi209at 37 MeV and the weak particle-core coupling

Abstract

Differential scattering cross-section data have been measured at 43 angles from ${11}^{\ifmmode^\circ\else\textdegree\fi{}}$ to ${160}^{\ifmmode^\circ\else\textdegree\fi{}}$ for 37-MeV neutrons incident on $^{209}\mathrm{Bi}$. 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 $^{3}\mathrm{H}$($d,n$)$^{4}\mathrm{He}$ 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 [A. J. Koning and J. P. Delaroche, Nucl. Phys. A 713, 231 (2003)] is modified, thus suggesting the need for global optical-model improvements at medium neutron energies.