Measurements on the excitation function and angular distribution of ${\mathrm{B}}^{10}(p, \alpha ){\mathrm{Be}}^7, {\mathrm{Be}}^{7*}$ have been carried out with apparatus which is an improvement over that used for previous measurements. Excitation functions have been measured at laboratory angles of 90° and 145° with respect to the bombarding beam, from 0.8 to 1.65 Mev. Angular distributions have been measured at 1.0, 1.2, 1.36, 1.5, and 1.63 Mev, and at 1.3, 1.5, and 1.63 Mev for the excited state. The excitation functions show resonances at 1.17 and 1.5 Mev for the ground state, and 1.55 Mev for the excited state transition. The resonances are superposed on a continuous isotropic background. The 1.17-Mev resonance shows nearly an isotropic distribution to the ground state. The 1.5-Mev state shows a distribution which is 1-0.53 ${cos}^2\theta$ with very small interference terms. The angular distributions leading to the excited state show a marked asymmetry with the backward angles being favored. The absolute cross section at laboratory 90°, $E_p=1.5\mathrm{}$ Mev for the ground state transition, is 21.1±4 mb/sterad. This value is in reasonable agreement with previous work.

The angular distributions are not inconsistent with an assignment of $\frac{3}{2^{-}}$ for the 9.70-Mev state and $\frac{7}{2^{+}}$ for the 10.06-Mev state in ${\mathrm{C}}^{11}$.

• Received 28 September 1955

DOI:https://doi.org/10.1103/PhysRev.101.298