$\beta$ decay of 31Mg: Extending the "island of inversion"
Résumé
The beta of 31Mg has been investigated at GANIL. The ions were implanted in a silicon detector array surrounded by germanium gamma detectors. beta particles and subsequent gamma rays have been observed. The 31Mg half-life has been measured (T_1/2=237pm25 ms) in good agreement with previously reported values. The decay scheme of 31Mg has been enriched with two new low-spin levels and seven new $\gamma$ transitions in 31Al. Most importantly, very weak feeding to the 31Al ground and lowest excited states has been established. These results are compared to new shell-model calculations in the sd-fp valence space, using an interaction that was modified in order to reproduce the recently established low-energy level scheme of 31Mg. A good agreement for all observables is found, supporting the idea that 31Al is outside and 31Mg is inside the so-called "island of inversion."