The 0° excitation functions for the reaction ${}_{}{}^9{}_{}{}^{}\mathrm{Be}(\alpha ,n){}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ leading to the ground and first excited states of ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ were measured between 1.69- and 6.44-MeV bombarding energy, while those for the second- and third-excited-state neutron groups were measured above 2.94- and 5.94-MeV bombarding energy, respectively. Angular distributions of the ground state and first two excited-state neutron groups were measured at 17 bombarding energies between 3.21 and 6.44 MeV, and for the third-excited-state neutron group they were measured at 6.24- and 6.44-MeV bombarding energy. The magnitude of the cross sections for the ground- and first-excited-state neutron groups agrees well with the larger of the two sets of conflicting magnitudes reported in the literature. Double-differential cross sections of the continuum of low-energy neutrons were measured as a function of angle and neutron energy for 10 bombarding energies ranging from 4.86 to 6.44 MeV. The features of the continuum are consistent with the sequential decay ${}_{}{}^9{}_{}{}^{}\mathrm{Be}+\alpha \to {}_{}{}^9{}_{}{}^{}\mathrm{Be}_{}^{*}{}_{}{}^{}+{\alpha }^{\prime }\to {}_{}{}^8{}_{}{}^{}\mathrm{Be}+n+{\alpha }^{\prime }$, proceeding through the 1.67-, 2.43-, and 3.04-MeV excited states in ${}_{}{}^9{}_{}{}^{}\mathrm{Be}$. The ratio of the populations of the first and second excited states in the ${}_{}{}^9{}_{}{}^{}\mathrm{Be}(\alpha ,n){}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ reaction was determined at 16 bombarding energies between 3.99 and 6.44 MeV.

• Received 25 June 1971

DOI:https://doi.org/10.1103/PhysRevC.5.738