The energy levels in ${\mathrm{B}}^{10}$ at 4.77 and 5.16 MeV have been studied by means of the reactions ${\mathrm{B}}^{11}({\mathrm{He}}^3,\alpha ){\mathrm{B}}^{10}$ and ${\mathrm{Li}}^6(\alpha ,\gamma ){\mathrm{B}}^{10}$. In measurements on the ${\mathrm{B}}^{11}({\mathrm{He}}^3,\alpha ){\mathrm{B}}^{10}$ reaction (${E_{\mathrm{He}}}^3=3.5\mathrm{}$ MeV), alpha particles populating states of ${\mathrm{B}}^{10}$ were observed at 90° in coincidence with (a) ${\mathrm{B}}^{10}$ recoil nuclei, (b) ${\mathrm{B}}^{10}$ recoils and gamma rays, and (c) decay alpha particles, by using two solid-state detectors and a NaI detector. Relative alpha-particle and gamma-ray branching intensities were determined for the decay of the 4.77- and 5.16-MeV states. The ratio of population intensities of the 5.16- and 5.11-MeV states was measured by using a Buechner-type magnetic spectrograph. In the ${\mathrm{Li}}^6(\alpha ,\gamma ){\mathrm{B}}^{10}$ reaction thick-target gamma-ray yields were measured at resonances for forming the 4.77- and 5.16-MeV states. For the 4.77-MeV state the angular distribution of the predominant 4.05-MeV gamma ray was determined, the 4.77-MeV ground-state transition was detected, and the angular distribution of the 4.77-MeV gamma ray was measured. The intensity of the ground-state gamma-ray branch from the 4.77-MeV level was measured to be (0.5±0.1)%, and the angular distribution of this transition in the ${\mathrm{Li}}^6(\alpha ,\gamma ){\mathrm{B}}^{10}$ reaction favors an assignment of $J^{\pi }=3^{+}$ to the 4.77-MeV state. Assignments of either $J^{\pi }=2^{+} or 3^{+}$ are allowed by the angular distribution of the 4.05-MeV transition from this state. $\frac{{\Gamma }_{\gamma }}{\Gamma }$ for the 4.77-MeV level was measured to be (2.3±0.3)×${10}^{-3\mathrm{}}$. For the $J^{\pi }=3^{+}$ assignment, partial widths for the 4.77-MeV level were measured to be ${\Gamma }_{\gamma }=0.033\mathrm{}\pm 0.006$ eV and ${\Gamma }_{\alpha }=14\mathrm{}\pm 3$ eV. The partial widths of the 5.16-MeV level were measured as ${\Gamma }_{\gamma }=2.9\mathrm{}\pm 1.1$ eV and ${\Gamma }_{\alpha }=0.44\mathrm{}\pm 0.09$ eV for an alpha-particle branch of (13±4)%. The properties of these and neighboring states are discussed in terms of the independent-particle model. Good agreement is found on some striking features but several points remain to be clarified.

• Received 18 October 1965

DOI:https://doi.org/10.1103/PhysRev.143.692