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

Precise reaction cross sections (sigma R) for (24- 38) Mg on C targets at energies around 240 MeV/nucleon have been measured at the Radioactive Isotope Beam Factory at RIKEN. The sigma R for (36-38) Mg have been measured for the first time. An enhancement of sR 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 sR for Mg-37 is especially large. It is shown by analysis using a recently developed theoretical method that this prominent enhancement of sR for Mg-37 should come from the p-orbital halo formation breaking the N = 28 shell gap.