Breakup Reactions of Neutron Drip Line Nuclei Near N=20

Coulomb breakup at intermediate energies is a useful experimental tool for investigating the microscopic structure of neutron drip-line nuclei. Here, results from the inclusive Coulomb breakup experiment of Ne-31 on a lead target at RIBF(RI Beam Factory) at RIKEN are presented. The experiment was performed as one of day-one campaign experiments at RIBF, using a Ca-48 primary beam at 345 MeV/nucleon. A unique feature of a halo nucleus is the enhanced electric dipole strength of the order of 1 W.u.(Weisskopf unit) at very low excitation energies around 1 MeV (soft El excitation). Owing to high sensitivity of the Coulomb breakup to the soft El excitation, a measurement of inclusive Coulomb breakup cross section can be used to identify the halo structure of a certain drip-line nucleus. We have indeed observed a strong enhancement of the Coulomb breakup cross section of 540(70) mb for Ne-31 on Pb at 230 MeV/nucleon, nearly as high as that for the known halo nucleus C-19, thereby giving evidence of the halo structure in Ne-31. The finding of a new halo structure for such a heavy system, compared to the known halo nuclei, is the first step for the understanding of halo phenomena along the neutron drip line towards heavier nuclei. We discuss also the change of shell structure in Ne-31, as a nucleus in the island of inversion.