The nuclear reactions ${\mathrm{Li}}^7(\alpha , n){\mathrm{B}}^{10}$ and ${\mathrm{Li}}^7(\alpha , {\alpha }^{\prime }){\mathrm{Li}}^{7*}$ have been studied for monoenergetic $\alpha$ particles from a Van de Graaff accelerator. The threshold in the ($\alpha , n$) reaction was measured to be 4.379 Mev which gives a $Q$ value of -2.788 Mev. Resonances in the yield of 0.477-Mev $\gamma$ radiation were observed at $\alpha$-particle energies of 1.91, 2.49, 3.06, 3.6, 4.39, 4.6, and 5.0 Mev. The inverse reaction ${\mathrm{B}}^{10}(n, \alpha ){\mathrm{Li}}^7$ was also studied by using monoenergetic neutrons with energies between 0.020 and 4.80 Mev. Resonances were observed at neutron energies of 0.53, 1.86, 2.8, and 4.1 Mev. Excited states in ${\mathrm{B}}^{11}$ from these experiments are indicated at 9.88, 10.25, 10.62, 10.97, 11.46, 11.6, 11.9, 13.2, 14.0, and 15.2 Mev.

• Received 5 August 1957

DOI:https://doi.org/10.1103/PhysRev.108.1025