We present simultaneously obtained data for the mirror reactions ${}_{}{}^{10}{}_{}{}^{}\mathrm{B}(\alpha , n_0){}_{}{}^{13}{}_{}{}^{}\mathrm{N}$ and ${}_{}{}^{10}{}_{}{}^{}\mathrm{B}(\alpha , p_0){}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ and interpret the yield ratio with the formula of Barker and Mann. All but one of the isospin-mixed levels emit neutrons more copiously than protons, although we might expect about half of them to emit protons more copiously. We also present ${}_{}{}^{10}{}_{}{}^{}\mathrm{B}(\alpha , p_i){}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ cross sections for groups which leave ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ in the ${\mathrm{½}}^{-}$ ground state; and in the ${\mathrm{½}}^{+}$ 3.086, ${\frac{3}{2}}^{-}3.684$, and ${\frac{5}{2}}^{+}3.854$ MeV excited states. We expanded the angular distributions in Legendre polynomials and fitted the coefficients at some of the resonances with compound nucleus scattering theory, obtaining spin-parity assignments: $1^{+}$ at $E_x\left({}_{}{}^{14}{}_{}{}^{}\mathrm{N}\right)=13.16, 2^{-} \mathrm{at} 13.24, (2^{+}, 2^{-}, 3^{+}) \mathrm{at} 13.67, \mathrm{and} (1^{+}, 1^{-}) \mathrm{at} 13.76$ MeV. As part of the calibration of the neutron spectrometer, we found the total ${}_{}{}^3{}_{}{}^{}\mathrm{He}(n, p){}_{}{}^3{}_{}{}^{}\mathrm{H}$ cross section is 422±58 mb for 3.5 MeV neutrons. This value is about 20% lower than currently accepted values.

NUCLEAR REACTIONS ${}_{}{}^{10}{}_{}{}^{}\mathrm{B}(\alpha , p_i)$ $i=0, 1, 2, 3$ ($\alpha , n_0$) $E=2-10\mathrm{}$ MeV; measured $\sigma (E, \theta )$; deduced ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$ levels, $J$, $\pi$, isospin impurity. Enriched targets, resolution 50 keV, $\theta =10-160\mathrm{}°$; Legendre polynomial expansion of $\sigma (E, \theta )$; absolute cross sections. Total $\sigma$ for ${}_{}{}^3{}_{}{}^{}\mathrm{He}(n, p)$ at $E_n=3.5\mathrm{}$ MeV.

• Received 1 July 1974

DOI:https://doi.org/10.1103/PhysRevC.11.1071