Cross sections for theLi7(p,n)Be7reaction between 4.2 and 26 MeV

Using pulsed-beam neutron time-of-flight spectrometry relative differential cross sections for ${}_{}{}^7{}_{}{}^{}\mathrm{Li}(p,n_0){}_{}{}^7{}_{}{}^{}\mathrm{Be}$(g.s.) and ${}_{}{}^7{}_{}{}^{}\mathrm{Li}(p,n_1){}_{}{}^7{}_{}{}^{}\mathrm{Be}_{}^{*}{}_{}{}^{}$ (0.431 MeV) have been measured over the laboratory angular range 3.5° to 159° and from an incident bombarding energy of 4.2 to 26 MeV. These cross sections have been integrated over angle and at 5 MeV the resulting integral was normalized to the absolute measurement of Macklin and Gibbons in order to obtain absolute differential and total cross sections for each neutron group. At energies above 6 MeV the 3.5° cross section for each group decreases monotonically, reaching a minimum at about 12 MeV. Both cross sections then increase, the ground-state cross section approaching a center-of-mass value of 15 mb/sr at 26 MeV. The forward-angle ratio of $n_1$ to $n_0$ neutrons remains around 30% from 8 to 26 MeV, obtaining a maximum of about 35% at 26 MeV. The integrated cross sections, on the other hand, both decrease from 6 MeV to the maximum energy. Neutrons from states in ${}_{}{}^7{}_{}{}^{}\mathrm{Be}$ at 4.55, 6.51, 7.19, and possibly 10.79 MeV as well as those from three-body breakup were also observed in this experiment.