Mass Measurements of Neutron-Deficient Yb Isotopes and Nuclear Structure at the Extreme Proton-Rich Side of the N=82 Shell

International audienceHigh-accuracy mass measurements of neutron-deficient Yb isotopes have been performed at TRIUMF using TITAN’s multiple-reflection time-of-flight mass spectrometer (MR-TOF-MS). For the first time, an MR-TOF-MS was used on line simultaneously as an isobar separator and as a mass spectrometer, extending the measurements to two isotopes further away from stability than otherwise possible. The ground state masses of Yb150,153 and the excitation energy of Ybm151 were measured for the first time. As a result, the persistence of the N=82 shell with almost unmodified shell gap energies is established up to the proton drip line. Furthermore, the puzzling systematics of the h11/2-excited isomeric states of the N=81 isotones are unraveled using state-of-the-art mean field calculation

The Nucleus 59Cu - Complex Structure, Shape Evolution, Exotic Decay Modes

High-spin states in the mass A~60 region were populated using the state-of-art gamma-ray spectrometers Gammasphere, Euroball, and GASP in conjunction with dedicated ancillary detectors. In particular, the 59Cu nucleus was studied in several experiments, and a very extensive level scheme was determined. It comprises more than 320 transitions connecting about 150 excited states. Relative to mass, it is the most extensive level scheme known to date. Next to the spherical states at low excitation energy eight regular sequences of high-energy gamma-ray transitions have been observed. They form rotational bands with various degree of deformation, which are interpreted in the light of the shell model and the configuration-dependent Cranked Nilsson-Strutinsky approach. One of the experiments was dedicated to the study of prompt particle decays. It revealed five prompt proton decays connecting five deformed states in three of the rotational bands in 59Cu with three spherical states in the daughter nucleus 58Ni. It is the first observation of the fine structure of the newly discovered prompt proton decay mode. The proton decays compete with the gamma decay-out from the second minimum of the nuclear potential into the low-spin spherical states in the first minimum of the potential. The discrete gamma decay-out mechanism of the yrast superdeformed band is investigated in detail. The nucleus 59Zn, the mirror partner of 59Cu, was identified for the first time, and the mirror symmetry of the T=1/2 A=59 pair is discussed

Evolution and Destruction of Shapes in 59Cu

An extensive high-spin level scheme has been established in 59Cu using a heavy-ion fusion evaporation reaction and the GAMMASPHERE multidetector array in conjunction with MICROBALL. Next to the spherical states at low excitation energy a large number of regular sequences of high-energy γ-ray transitions have been observed, which form rotational bands with various degree of deformation. For the yrast superdeformed band about 90% of the intensity of the discrete γ decay-out, distributed over about 30 decay paths, is known, which allows for a detailed study of this decay-out process. Two of the deformed bands were found to decay by prompt proton emission into two different spherical states of 58Ni, in direct competition with the γ decay-out proces

Nonyrast States in the Odd-odd N = Z Nucleus 62Ga

Low-lying excited states in the odd-odd N = Z nucleus 62Ga have been investigated following the heavy-ion fusion-evaporation reaction 40Ca(24Mg,pn)62Ga near the Coulomb barrier. Special emphasis is devoted to the search for nonyrast states. The extended decay scheme of 62Ga is compared to spherical shell-model calculations employing the pf5/2g9/2 valence space

Observation of a Core-Excited E4 Isomer in 98Cd

A core-excited I = (12+) spin-gap isomer was identified in 98Cd in an experiment at EUROBALL IV. It was found to feed the known I = (8+) seniority isomer by an E4 transition. Half-lives of T1/2 = 0.23() µs and 0.17() µs were measured for the two states at Ex = 6635 keV and 2428 keV, respectively. From the excitation energy of the core-excited isomer a 100Sn shell gap of 6.46(15) MeV is inferred. The measured E4 and E2 strengths, 100Sn core excitations and the origin of empirical polarization charges are discussed in the framework of large-scale shell model calculations. An E2 polarization charge for protons of e<0.4 e is found, which corresponds to the empirical value e = 0.45() e in the pure proton hole valence space

Complete Spectroscopy in High-spin Cranking Calculations

Exact and approximate quantum numbers of the cranked Nilsson-Strutinsky (CNS) formalism are exploited to calculate excited bands in fixed configurations with the energy of the individual bands minimized with respect to deformation for all spin values. The formalism is applied to Cu-59, where all bands which appear important in the decay out of the superdeformed band are calculated

Survey of E1 Transitions in the Mass A~60 Region

A survey of parity-changing E1 transitions has been pursued in N>~Z nuclei near 56Ni using data from an EUROBALL experiment. Linear polarization measurements have been combined with angular correlations of coincident gamma rays to determine the electromagnetic character of numerous transitions. The impact of the results on shell-model parametrizations is briefly discussed

Competing Decay-out Mechanisms of the Yrast Superdeformed Band in 59Cu

This contribution reports on the decay-out of the yrast superdeformed band in 59Cu. It decays by multiple γ-ray transitions into low-spin spherical states in the first minimum of the nuclear potential in 59Cu, and, in competition, by emitting two prompt protons into a spherical state in 58Ni. For the first time in A ~ 60, the role of doorway states in the course of the decay-out is discusse