Structure evolution of ground and excited states in the exotic nucleus 22Al
Abstract
Recent experimental studies on proton-rich nuclei in the sd shell have revealed intriguing near-threshold phenomena, including exotic structures associated with mirror-symmetry breaking. In particular, a halo-like structure has been suggested for the 1+ state of 22Al based on the large isospin asymmetry observed in the 22Si/22O mirror Gamow-Teller transitions. Recent mass measurements further indicate that the ground state of 22Al is weakly bound, with a single-proton separation energy of about 100 keV. To investigate how the continuum affects the structure and decay properties of this proton-dripline nucleus, we employ the state-of-the-art Gamow shell model. This approach utilizes valence-space effective interactions and operators derived from chiral forces. Our calculations identify the ground state of 22Al as a 4+ state, with a 3+ state as the first excitation. Despite their diffuse nature under weak binding, the Thomas-Ehrman shift for these states is found to be negligible due to their small s-wave components. In contrast, the excited 11+ state possesses a significantly larger s-wave component, resulting in a more pronounced halo-like structure.