Excitation functions for the elastic scattering of protons by ${\mathrm{B}}^{10}$ have been measured at center-of-mass scattering angles near 90°, 125°, and 160° for proton energies between $E_p=0.15\mathrm{}$ MeV and $E_p=3.0\mathrm{}$ MeV. Scattering angular distributions were measured at 43 selected energies in this range. An excitation function for the reaction ${\mathrm{B}}^{10}(p, {\alpha }_0){\mathrm{Be}}^7$ was also measured between $E_p=1.5\mathrm{}$ MeV and $E_p=2.6\mathrm{}$ MeV at a laboratory angle of 90°. The atomic stopping cross section of boron for protons has been determined between $E_p=0.1\mathrm{}$ MeV and $E_p=3.0\mathrm{}$ MeV.

The elastic scattering excitation functions exhibit conspicuous anomalies at $E_p=1.50\mathrm{}$ MeV and $E_p=2.180\mathrm{}$ MeV. The ${\alpha }_0$ transition to the ground state of ${\mathrm{Be}}^7$ is also resonant at $E_p=2.180\mathrm{}$ MeV. The behavior of the cross sections in these regions has been analyzed in terms of compound states of ${\mathrm{C}}^{11}$. Satisfactory agreement is achieved with level assignments of $J^{\pi }=\frac{7}{2^{+}}$ with $E_R=1.50\mathrm{}$ MeV, ${\Gamma }_p=90\mathrm{}$ keV, ${\Gamma }_T=250\mathrm{}$ keV; and $J^{\pi }=\frac{9}{2^{+}}$ with $E_R=2.180\mathrm{}$ MeV, ${\Gamma }_p=100\mathrm{}$ keV, ${\Gamma }_{\alpha 0}=100\mathrm{}$ kev, and ${\Gamma }_T=200\mathrm{}$ keV. Although complete analysis of the scattering is hindered by the influence of unknown background processes, the negative parity assignment for the previously reported state at $E_p=1.17\mathrm{}$ MeV, derived from other reaction experiments, appears inconsistent with the scattering.

• Received 21 May 1962

DOI:https://doi.org/10.1103/PhysRev.128.315