$\beta$-neutron time-of-flight techniques have been used to detect a third and previously unobserved neutron group in the decay of ${}_{}{}^{13}{}_{}{}^{}\mathrm{B}$ corresponding to a (0.022 ± 0.007)% $\beta$-ray branch to the 9.90-MeV state of ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$. The $log\mathrm{ft}$ of 4.95 ± 0.12 for this branch agrees with the $log\mathrm{ft}$ of 5.18 ± 0.14 for the analog ${}_{}{}^{13}{}_{}{}^{}\mathrm{O}$→${}_{}{}^{13}{}_{}{}^{}\mathrm{N}$ transition, and thus confirms a previous assignment of the 9.90-MeV ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ state as the $J^{\pi }={\frac{3}{2}}^{-}$ analog of the 9.52-MeV state in ${}_{}{}^{13}{}_{}{}^{}\mathrm{N}$.

RADIOACTIVITY ${}_{}{}^{13}{}_{}{}^{}\mathrm{B}$; measured $\beta$-neutron time-of-flight spectrum; deduced $\beta$ branches, $log\mathrm{ft}$; compared with ${}_{}{}^{13}{}_{}{}^{}\mathrm{O}$ mirror decay.

• Received 24 April 1974

DOI:https://doi.org/10.1103/PhysRevC.10.935