Investigation of Exotic Structure of the Largely Deformed Nucleus ²³Al in the Relativistic-Mean-Field Model

A candidate for proton halo nucleus ²³Al is investigated based on the constrained calculations in the framework of the deformed relativistic mean field (RMF) model with the NL075 parameter set. It is shown by the constrained calculations that the ground state of ²³Al has a large deformation that corresponds to the prolate shape. With that large deformation, the non-constrained RMF calculation predicts that there appears an inversion between the 2s_1/2 211 and 1d_5/2 202 shells. The valence proton of ²³Al is weakly bound and occupies 2s_1/2 211 and 1d_5/2 202 with the weights of 56% and 29%, respectively. The calculated RMS radius for matter is in agreement with the experimental one. It is also predicted that the difference between the proton RMS radius and the neutron one is very large. This suggests that there exists a proton halo in ²³Al.