Neutrons from Proton Bombardment of Lithium

Relative cross sections for the production of neutrons from the proton bombardment of ${\mathrm{Li}}^7$ have been measured from 3 to 13 MeV bombarding energy. Time-of-flight spectrometry was used to resolve the groups of neutrons going to various states in ${\mathrm{Be}}^7$. The cross section for neutrons leaving ${\mathrm{Be}}^7$ in its ground state shows a peak at 5 MeV and then decreases rapidly as the energy is increased, while the number of neutrons leaving ${\mathrm{Be}}^7$ in its first excited state decreases fairly uniformly over the whole energy range. The angular distributions for both groups show considerable structure below 6 MeV but become isotropic at higher bombarding energies. From 9 to 13 MeV the zero-degree yield of neutrons leaving ${\mathrm{Be}}^7$ in its excited state at 4.53 MeV was measured. At the higher proton energies several breakup reactions are energetically possible, but no continuum neutrons from them were observed at 10 MeV bombarding energy.