Interaction of Neutrons with ⁹Be at 14.6 MeV — The Four-Body Breakup 2n + 2α

A metallic ⁹Be target was bombarded with 14.6-MeV neutrons. Double-differential cross sections were measured for the (n, α) reaction in the angular range from 0 to 100 deg. The measured alpha-particle spectra and complementary neutron spectra from the literature were analyzed in terms of a combination of sequential and simultaneous breakups. The results show that ∼50% of the total inelastic cross section is due to simultaneous breakup n + ⁹Be →  n + α + ⁵He, while the remainder is mainly due to neutron inelastic scattering to the three excited states of ⁹Be: 2.43, 6.76, and 11.28 MeV. This analysis gives evidence of the validity of the constant matrix element model and contradicts evaluations that ignore the simultaneous breakup contributions.