The spectrum of gamma radiation emitted when ${\mathrm{B}}^{11}$ is bombarded by protons has been investigated with a NaI scintillation counter. Capture gamma rays have been found which occur in a direct transition to the ground state of ${\mathrm{C}}^{12}$ and a cascade transition through a level in ${\mathrm{C}}^{12}$ at 4.45 Mev. Yield curves for these gamma rays have been obtained for proton energies up to 2.8 Mev, and the cross sections for emission of the various gamma rays are given. In addition to the well-known resonance at 0.163 Mev, new resonances have been found at 0.675 Mev with $\Gamma =0.33\mathrm{} \mathrm{Mev}\mathrm{and} 1.388 \mathrm{Mev}$ with $\Gamma =1.27\mathrm{}$ Mev. Spin and parity assignments for these states which are deduced from the results of this and the ${\mathrm{B}}^{11}(p, \alpha ){\mathrm{Be}}^8$ reactions are $2^{-}$ (or $3^{+}$) and $1^{-}$, respectively. A 2.13-Mev gamma ray has also been observed, which is produced in an inelastic scattering reaction involving the first excited state of ${\mathrm{B}}^{11}$. This reaction exhibits a resonance at 2.664 Mev with a width of 48 kev. The cross section at resonance is 3.1×${10}^{-26\mathrm{}}$ ${\mathrm{cm}}^2$.

• Received 20 April 1953

DOI:https://doi.org/10.1103/PhysRev.91.599