Halo Structure of Nucleus ²³Al

The recently measured reaction cross section of ²³Al is analysed in the Glauber model with an optical limit or few-body approach. It is found that the conventional fixed core-plus-nucleon model for halo nuclei is unable to explain the observed abnormally large reaction cross section of ²³Al by any selection of the halo nucleon configurations. The reaction cross section of ²³Al can be described when the core size is enlarged, although the Coulomb barrier largely hinders the formation of a halo structure for proton-rich nuclei. This is consistent with the case in s-d shell neutron-rich nuclei, where an enlarged core was proposed to explain both the reaction cross section and longitudinal momentum distribution data.