Evidence of halo structure in 37Mg observed via reaction cross sections and intruder orbitals beyond the island of inversion

Precise reaction cross sections (σ_R) for ^Mg-38₂₄ on C targets at energies around 240 MeV/nucleon have been measured at the Radioactive Isotope Beam Factory at RIKEN. The σ_R for ^Mg-38₃₆ have been measured for the first time. An enhancement of σ_R compared to the systematics for spherical stable nuclei has been observed, especially in the neutron-rich region, which reflects the deformation of those isotopes. In the vicinity of the drip line the σ_R for ³⁷Mg is especially large. It is shown by analysis using a recently developed theoretical method that this prominent enhancement of σ_R for ³⁷Mg should come from the p -orbital halo formation breaking the N =28 shell gap.