Resonance-decay spectroscopy is used to study particle-unbound excited states produced in interactions of $E/A=50$ MeV ${}^{12}\mathrm{Be}$ on polyethylene and carbon targets. The particle-unbound states are produced in a variety of reaction mechanisms, ranging from projectile fragmentation to proton pickup. New proton-decaying excited states are observed in ${}^9\mathrm{Li}$($E^{*}=14.1\pm 0.1\hspace{0.5em}\mathrm{MeV}$, $\Gamma =207\pm 49$ keV) and ${}^{10}\mathrm{Be}$($E^{*}=20.4\pm 0.1\hspace{0.5em}\mathrm{MeV}$, $\Gamma =182\pm 74$ keV). In addition a new $\alpha$-decaying state is observed in ${}^{13}\mathrm{B}$($E^{*}=13.6\pm 0.1\hspace{0.5em}\mathrm{MeV}$, $\Gamma ⩽320$ keV). Also found was a ${}^8\mathrm{Be}$ state with $E^{*}=23\hspace{0.5em}\mathrm{MeV}$, $\Gamma =616\pm 30$ keV, which decays to the $p+{}^3\mathrm{H}+\alpha$ channel. Correlation between the fragments indicates that the decay is initiated by a proton emission to the 4.63-MeV state of ${}^7\mathrm{Li}$ and the spin of the state is $J>2$. A second $T=2$ state was confirmed in ${}^{12}\mathrm{B}$ at 14.82 MeV, which decays to the $p+{}^{11}\mathrm{Be}$, ${}^3\mathrm{H}+{}^9\mathrm{Be}$, and $\alpha +{}^8\mathrm{Li}$ channels. Its width was found to be $\Gamma ⩽100$ keV and its spin is consistent with $J^{\pi }=2^{+}$.

• Received 2 September 2008

DOI:https://doi.org/10.1103/PhysRevC.78.054307