Beta-Decay Study of the T-Z =-2 Proton-Rich Nucleus Mg-20

The beta decay of the drip-line nucleus Mg-20 gives important information on key astrophysical resonances in 20Na, which are relevant to the onset of the rapid proton capture process. A detailed beta-decay spectroscopic study of 20Mg 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 20Mg, the excitation energies, the branching ratios, and the log ft values for the states in Na-20 populated in the beta decay of Mg-20. A new proton branch was observed and the corresponding excited state in 20Na was proposed. The large isospin asymmetry for the mirror decays of Mg-20 and O-20 was also well reproduced. To resolve the long-standing problem about the astrophysically interesting 2645 keVresonance in Na-20 convincingly, a higher-statistics measurement may still be needed.