{beta} decay of {sup 31}Mg: Extending the 'island of inversion'

The {beta} decay of {sup 31}Mg 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 {sup 31}Mg half-life has been measured (T{sub 1/2}=237{+-}25 ms) in good agreement with previously reported values. The decay scheme of {sup 31}Mg has been enriched with two new low-spin levels and seven new {gamma} transitions in {sup 31}Al. Most importantly, very weak feeding to the {sup 31}Al 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 {sup 31}Mg. A good agreement for all observables is found, supporting the idea that {sup 31}Al is outside and {sup 31}Mg is inside the so-called 'island of inversion'.