Inelastic Scattering of Alpha Particles by Lithium

The inelastic scattering of alpha particles by ${\mathrm{Li}}^7$ leading to the formation of the 478-kev state of ${\mathrm{Li}}^7$ has been studied by observation of the gamma ray emitted from that state. Singly charged helium ions accelerated by an electrostatic generator were used to determine the yield of the reaction up to an energy of 2.8 Mev. The excitation curve shows a resonance at 1.889±0.010 Mev, with a width of 200 kev and a peak cross section of 0.11±0.02 barn, and another broad resonance at 2.50±0.03 Mev with a peak cross section of 0.08±0.015 barn. These resonances correspond to levels of ${\mathrm{B}}^{11}$ at 9.86 Mev and 10.23 Mev. The thick target yield at $E_{\alpha }=2.3\mathrm{}$ Mev is $1.5\times {10}^{-6\mathrm{}}\frac{\gamma }{\alpha }$. The Doppler shift of the emitted gamma ray furnishes an upper limit of the lifetime for the 478-kev excited state of ${\mathrm{Li}}^7$.