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Advanced nuclear structure models predict the presence of the shell closures N = 14, 16 in neutron-rich O isotopes rather than N = 20. Spectroscopic investigations performed at the neutron drip line have recently confirmed such predictions showing that the 24O is a doubly magic nucleus (Z = 8, N = 16). Predictions within the shell model calculation for the 23,24O ground state have been confirmed measuring their spectroscopic factors. Results obtained in one-neutron removal reactions performed by using in-flight radioactive ion beams produced at the Fragment Separator FRS of GSI are reported. [ABSTRACT FROM AUTHOR]

Dipole strength distributions were determined for the neutron-rich nuclei 129–132Sn and 133,134Sb from electromagnetic excitation in an experiment using the FRS-LAND setup. For all nuclei, a sizeable fraction of “pygmy” dipole strength at excitation energies well below the giant dipole resonance was observed. The integrated low-lying dipole strength of the nuclei with low neutron separation energies can be compared to results for stable nuclei (e.g. N = 82 isotopes) determined for the energy regime of 5–9 MeV. A clear increase of the dipole strength with increasing asymmetry of the nuclei is observed. Comparing the ratio of the low-lying dipole over the giant dipole strength to recent relativistic mean field calculations, values for the parameters a4 and p0 of the symmetry energy and for the neutron skin thickness are derived. Averaged over 130Sn and 132Sn we extract ā4 = 31.8±1.3 MeV and p0 = 2.2±0.5 MeV/fm3. The neutron skin sizes are determined to Rn-Rp = 0.23±0.03 fm and 0.24±0.03 fm for 130Sn and 132Sn, respectively. For 208Pb a neutron skin thickness of Rn-Rp = 0.18±0.035 fm follows, when applying the same method and using earlier published experimental findings on the dipole strength. [ABSTRACT FROM AUTHOR]

Heavy neutron-rich nuclei close to the neutron closed shell N = 126 were produced by fragmentation of a 1 A GeV 208Pb beam in a beryllium target at the Fragment Separator at GSI. Around 30 heavy neutron-rich isotopes have been synthesized for the first time and the half-lives of some of them have been determined. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

One-nucleon removal reactions at relativistic energies have been used as spectroscopic tool to obtain information about the ground state properties of several neutron-rich isotopes in the sd-shell. Using the FRS at GSI, the longitudinal momentum distributions of the emerging fragments after one-nucleon removal cross-sections were measured. The relative contributions of the remaining fragments in their ground and excited states have been determined from measurements of γ rays in coincidence with the longitudinal momentum distributions. The interesting case of 23O will be directly address. The interpretation of our experimental results in the framework of a simple theoretical model will favours a spin and parity assignment of 1/2+ for the 23O ground state in agreement with shell model predictions. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

An experiment was performed using the FRS-LAND setup at GSI to study the dipole strength distributions above neutron separation threshold for neutron-rich Ni isotopes. Measurements, using the same experimental setup, were also carried out to extract single particle occupancies via knockout reactions to investigate the structure and magicity of the neutron-rich Ni isotopes. The status of the data analysis and preliminary results are presented. [ABSTRACT FROM AUTHOR]