β -decay study of the Tz=−2 proton-rich nucleus Mg20

The $\ensuremath{\beta}$ decay of the drip-line nucleus $^{20}\mathrm{Mg}$ gives important information on key astrophysical resonances in $^{20}\mathrm{Na}$, which are relevant to the onset of the rapid proton capture process. A detailed $\ensuremath{\beta}$-decay spectroscopic study of $^{20}\mathrm{Mg}$ was performed by a continuous-implantation method. A detection system was specially developed for charged-particle decay studies, giving improved spectroscopic information including the delayed proton energies, the half-life of $^{20}\mathrm{Mg}$, the excitation energies, the branching ratios, and the $logft$ values for the states in $^{20}\mathrm{Na}$ populated in the $\ensuremath{\beta}$ decay of $^{20}\mathrm{Mg}$. A new proton branch was observed and the corresponding excited state in $^{20}\mathrm{Na}$ was proposed. The large isospin asymmetry for the mirror decays of $^{20}\mathrm{Mg}$ and $^{20}\mathrm{O}$ was also well reproduced. To resolve the long-standing problem about the astrophysically interesting 2645 keV resonance in $^{20}\mathrm{Na}$ convincingly, a higher-statistics measurement may still be needed.