R. Lucas

Isomer spectroscopy of neutron rich 190W116

Abstract Gamma-rays de-exciting a millisecond isomer in the neutron-rich nucleus 190 74 W 116 have been observed following relativistic projectile fragmentation of a 1xa0GeV per nucleon 208 Pb beam. The isomeric decay populates the ground-state rotational band, with energies that indicate a significant deformation change at Z =74 for the N =116 isotones. The successful application of the projectile fragmentation technique in a region of deformed nuclei opens up the prospect of exploiting K -isomer decays to probe the evolution of collective nuclear structure far from the valley of beta stability.

High‐spin states in the neutron‐rich N = 50 region: nuclear structure close to 78Ni

The spectroscopy of fission fragments, obtained by the 18O+208Pb fusion‐fission reaction at 85 MeV bombarding energy, has been performed with the Euroball IV γ‐array. High‐spin states in many neutron‐rich Se, Br, Kr and Rb of the 78Ni region nuclei have been identified for the first time. Several physical aspects which govern the nuclear structure in this mass region are underlined thanks to the new results. Among those, empirical values of the residual proton‐neutron interactions have been extracted for the πf5/2⊗vd5/2 and πp3/2⊗vd5/2 configurations.The spectroscopy of fission fragments, obtained by the 18O+208Pb fusion‐fission reaction at 85 MeV bombarding energy, has been performed with the Euroball IV γ‐array. High‐spin states in many neutron‐rich Se, Br, Kr and Rb of the 78Ni region nuclei have been identified for the first time. Several physical aspects which govern the nuclear structure in this mass region are underlined thanks to the new results. Among those, empirical values of the residual proton‐neutron interactions have been extracted for the πf5/2⊗vd5/2 and πp3/2⊗vd5/2 configurations.

High‐Spin States of 84,85Br: Mapping the Proton Sub‐Shells towards 78Ni

The 84,85Br nuclei have been produced as fission fragments in the fusion reaction 18O+208Pb at 85 MeV bombarding energy and studied with the Euroball IV array. The high‐spin states of the odd‐odd 84Br nucleus have been identified for the first time. From angular correlation analysis, spin values have been assigned to most of the 85Br excited states up to 4 MeV. All observed states in 84,85Br can be described by various proton excitations involving at least the two sub‐shells (πf5/2 and πp3/2) located just above the Zu2009=u200928 shell closure.

Experimental Sign of a Weakening of the N=50 Spherical Shell Gap

High‐spin states of 84Se, produced as a fission fragment in the fusion‐fission reaction 18O+208Pb, have been identified for the first time thanks to the EUROBALL IV array. The excitation energies of three of these states, interpreted as being due to the (νg9/2−1u2009νd5/2+1) neutron‐core excitation, give new insights about the evolution of the N=50 shell gap at the vicinity of 78Ni.

In‐Beam γ‐Ray Spectroscopy of the N=50 Isotones on the Neutron‐Rich Side

High‐spin states of 84Se, produced as a fission fragment in the fusion‐fission reaction 18O+208Pb and studied with the EUROBALL IV array, have been identified for the first time. Their interpretation gives new insights about the evolution of the N=50 shell gap at the vicinity of 78Ni. To characterize this evolution, it would be worth using a new device devoted to the high‐spin studies of neutron‐rich nuclei produced by asymetric fission modes. Such dedicated studies are reported in a second part.