Using an on-line mass spectrometer the decay properties of the $T_z\ge \frac{5}{2}$ nuclei ${}_{}{}^{11}{}_{}{}^{}\mathrm{Li}$, ${}_{}{}^{27-31}{}_{}{}^{}\mathrm{Na}$, ${}_{}{}^{29,30}{}_{}{}^{}\mathrm{Mg}$ were studied. The new isotope ${}_{}{}^{30}{}_{}{}^{}\mathrm{Mg}$ ($T_{\frac{1}{2}}=1200\mathrm{}\pm 500$ msec) identified by $\beta$ counting. For the other isotopes the half-lives were remeasured by three independent methods with improved precision. By recording $\beta$-coincident $\gamma$ spectra, the decays of ${}_{}{}^{27-29}{}_{}{}^{}\mathrm{Na}$ were studied, leading to a $1^{+}$ assignment for the ${}_{}{}^{28}{}_{}{}^{}\mathrm{Na}$ ground state. By simultaneous $\beta$ and neutron multiscaling the delayed neutron emission probabilities $P_n$ were determined for ${}_{}{}^{11}{}_{}{}^{}\mathrm{Li}$ and ${}_{}{}^{27-31}{}_{}{}^{}\mathrm{Na}$. The following half-lives (msec) and $P_n$ values (%) were found (errors see text): ${}_{}{}^{11}{}_{}{}^{}\mathrm{Li}$ (8.5/60.8), ${}_{}{}^{27}{}_{}{}^{}\mathrm{Na}$ (304/0.08), ${}_{}{}^{28}{}_{}{}^{}\mathrm{Na}$ (30.5/0.58), ${}_{}{}^{29}{}_{}{}^{}\mathrm{Na}$ (42.9/15.1), ${}_{}{}^{30}{}_{}{}^{}\mathrm{Na}$ (53.0/33.1), ${}_{}{}^{31}{}_{}{}^{}\mathrm{Na}$ (16.9/30).

RADIOACTIVITY ${}_{}{}^{9,11}{}_{}{}^{}\mathrm{Li}$, ${}_{}{}^{27,28,29,30,31}{}_{}{}^{}\mathrm{Na}$, ${}_{}{}^{29,30}{}_{}{}^{}\mathrm{Mg}$; measured $T_{\frac{1}{2}}$, $E_{\beta }$, $\beta \gamma$ coin, delayed neutrons; deduced $E_{\gamma }$, $I_{\gamma }$, $log\mathrm{ft}$, $Q$, $J$, $\pi$, $P_n$. On-line mass separation.

• Received 28 May 1974

DOI:https://doi.org/10.1103/PhysRevC.10.1181