The first spectroscopic study for the $\beta$ decay of ${}^{21}\mathrm{N}$ is carried out based on $\beta –n$, $\beta –\gamma$, and $\beta –n–\gamma$ coincidence measurements. The neutron-rich ${}^{21}\mathrm{N}$ nuclei are produced by the fragmentation of the $E/A=68.8$ MeV ${}^{26}\mathrm{Mg}$ primary beam on a thick ${}^9\mathrm{Be}$ target and are implanted into a thin plastic scintillator that also plays the role of $\beta$ detector. The time of flight of the emitted neutrons following the $\beta$ decay are measured by the surrounding neutron sphere and neutron wall arrays. In addition, four clover germanium detectors are used to detect the $\beta$-delayed $\gamma$ rays. Thirteen new $\beta$-delayed neutron groups are observed with a total branching ratio of $90.5\pm 4.2\%$. The half-life for the $\beta$ decay of ${}^{21}\mathrm{N}$ is determined to be $82.9\pm 7.5$ ms. The level scheme of  ${}^{21}\mathrm{O}$ is deduced up to about 9 MeV excitation energy. The experimental results for the $\beta$ decay of ${}^{21}\mathrm{N}$ are compared to the shell-model calculations.

• Received 22 December 2008

DOI:https://doi.org/10.1103/PhysRevC.80.054315