We report the first observation of the beta decay of ${}_{}{}^9{}_{}{}^{}\mathrm{C}$ to the ground state and to two low-lying excited states of ${}_{}{}^9{}_{}{}^{}\mathrm{B}$. Branching ratios to these states were measured, and a previously reported branch to a level near 12 MeV was confirmed. The branching ratio to the $J^{\pi }$${=(3/2\mathrm{}}^{\mathrm{-}}$ ground state is 60±10 %, and the branching ratios to the narrow ${(5/2\mathrm{}}^{\mathrm{-}}$ level at 2.36 MeV and to the broad ${1/2}^{\mathrm{-}}$ level near 2.9 MeV are 17±6 % and 11±5 %, respectively. Because of the three-body nature of the ${}_{}{}^9{}_{}{}^{}\mathrm{B}$ decay, the ${}_{}{}^9{}_{}{}^{}\mathrm{C}$ ions were implanted in the active volume of silicon detectors, and the total decay energies of the states in ${}_{}{}^9{}_{}{}^{}\mathrm{B}$ were directly measured. We compare these results to shell model calculations, to the analog decay of ${}_{}{}^9{}_{}{}^{}\mathrm{Li}$ to ${}_{}{}^9{}_{}{}^{}\mathrm{Be}$, and to the ${}_{}{}^9{}_{}{}^{}\mathrm{Be}$(p,n${)}^9$B reaction. The comparison to ${}_{}{}^9{}_{}{}^{}\mathrm{Li}$ decay indicates an asymmetry in the beta-decay matrix elements to the ${(5/2\mathrm{}}^{\mathrm{-}}$ level larger than any such asymmetry previously observed.

• Received 7 May 1987

DOI:https://doi.org/10.1103/PhysRevC.37.766