The delayed neutron emitters ${}_{}{}^{16}{}_{}{}^{}\mathrm{C}$ and ${}_{}{}^{17}{}_{}{}^{}\mathrm{N}$ have been studied with a ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ neutron detector and $\gamma$ radiations have been measured with a Ge(Li) detector. ${}_{}{}^{16}{}_{}{}^{}\mathrm{C}$ was formed in the reaction ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}$(${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$)${}_{}{}^{16}{}_{}{}^{}\mathrm{C}$ with 56-MeV ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ ions, and also in the reaction ${}_{}{}^{11}{}_{}{}^{}\mathrm{B}({}_{}{}^7{}_{}{}^{}\mathrm{Li},2\mathrm{}p){}_{}{}^{16}{}_{}{}^{}\mathrm{C}$ with 40-MeV ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$ ions. The thermalized neutrons following both reactions yield together a ${}_{}{}^{16}{}_{}{}^{}\mathrm{C}$ half-life of 0.747 ± 0.008 sec with the well-known 4.17-sec ${}_{}{}^{17}{}_{}{}^{}\mathrm{N}$ activity as an accompaniment formed in the ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}$(${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^{17}{}_{}{}^{}\mathrm{N}$)${}_{}{}^{15}{}_{}{}^{}\mathrm{N}$ and ${}_{}{}^{11}{}_{}{}^{}\mathrm{B}({}_{}{}^7{}_{}{}^{}\mathrm{Li},p){}_{}{}^{17}{}_{}{}^{}\mathrm{N}$ reactions. The neutron spectra in a bare ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ detector contain ${}_{}{}^{16}{}_{}{}^{}\mathrm{C}$ lines of 0.79 ± 0.03 MeV and 1.72 ± 0.05 MeV with relative intensities $\frac{I_{0.79}}{I_{1.72}}=5.4\mathrm{}\pm 0.7$ in addition to ${}_{}{}^{17}{}_{}{}^{}\mathrm{N}$ peaks. The ${}_{}{}^{16}{}_{}{}^{}\mathrm{C}$ neutron groups are assigned to the $\beta$ decay to the known 3.36- and 4.32-MeV $1^{+}$ states of ${}_{}{}^{16}{}_{}{}^{}\mathrm{N}$ with branches of 84.4 ± 1.7% and 15.6 ± 1.7%, respectively.A search for $\gamma$ rays associated with ${}_{}{}^{16}{}_{}{}^{}\mathrm{C}$ forbidden $\beta$ decay to the $0^{-}$, $3^{-}$, and $1^{-}$ levels of ${}_{}{}^{16}{}_{}{}^{}\mathrm{N}$ at 0.121, 0.297, and 0.397 MeV, respectively, gave upper limits of 0.5%, 0.5%, and 0.7% for the respective branching ratios ($log\mathrm{ft}>\mathrm{}6.85, >6.83, \mathrm{and} >6.64\mathrm{}$, respectively). The $log\mathrm{ft}$ values for $\beta$ decay to the 3.36- and 4.32-MeV states, 3.551 ± 0.012 and 3.83 ± 0.05, respectively, compare with preliminary theoretical values of 6.49 and 3.94, respectively, due to Millener. Separate studies were made of ${}_{}{}^{17}{}_{}{}^{}\mathrm{N}$ decay, formed in the ${}_{}{}^{15}{}_{}{}^{}\mathrm{N}\mathrm{}(t,p)\mathrm{}{}_{}{}^{17}{}_{}{}^{}\mathrm{N}$ reaction at $E_t=3.0\mathrm{}$ MeV. By using an empirical neutron efficiency function, established for the ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ detector with the ${}_{}{}^3{}_{}{}^{}\mathrm{H}\mathrm{}(p,n)\mathrm{}{}_{}{}^3{}_{}{}^{}\mathrm{He}$ reaction, $\beta$-ray branches of ${}_{}{}^{17}{}_{}{}^{}\mathrm{N}$ to the ${}_{}{}^{17}{}_{}{}^{}\mathrm{O}$ neutron-emitting states at 4.55, 5.38, and 5.94 MeV were found to be 39.2 ± 2.0%, 48.0 ± 1.5%, and 7.9 ± 0.3%, respectively, in disagreement with two previously reported measurements. $\gamma$-ray measurements on ${}_{}{}^{17}{}_{}{}^{}\mathrm{N}$ with a Ge(Li) detector yielded the following: ratio of $\beta$-ray branching intensities $\frac{B_{871}}{B_{3055}}=8.6\mathrm{}\pm 0.4$; $B_{3841}<7\mathrm{}\times {10}^{-5\mathrm{}}$ corresponding to $log\mathrm{ft}>\mathrm{}8.5\mathrm{}$ for this $\beta$-ray branch, thereby more firmly fixing the ${}_{}{}^{17}{}_{}{}^{}\mathrm{N}$ spin as $J^{\pi }={\frac{1}{2}}^{-}$; energy of ${}_{}{}^{17}{}_{}{}^{}\mathrm{O}$ second-excited state 3055.2 ± 0.3 keV; and ground-state $\gamma$-ray branch from the 3055.2-keV level < 1.5%. The mirror $\beta$ decays of the $A=17\mathrm{}$ system are discussed. An incidental result is a half-life of 178.3 ± 0.4 msec for ${}_{}{}^9{}_{}{}^{}\mathrm{Li}$ formed in the $t({}_{}{}^7{}_{}{}^{}\mathrm{Li},p){}_{}{}^9{}_{}{}^{}\mathrm{Li}$ reaction with 20-40-MeV ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$ ions.

RADIOACTIVITY ${}_{}{}^{16}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{17}{}_{}{}^{}\mathrm{N}$; measured $t_{\frac{1}{2}}$, $E_n$, $I_n$, $I_{\gamma }$; deduced $log\mathrm{ft}$, decay schemes; compared with theory. ${}_{}{}^9{}_{}{}^{}\mathrm{Li}$; measured $t_{\frac{1}{2}}$.

• Received 29 October 1975

DOI:https://doi.org/10.1103/PhysRevC.13.835