High spin states in ⁸⁰Sr have been studied using the techniques of in-beam γ-ray spectroscopy. The reaction used was ⁵⁴Fe(²⁹Si, 2pn)⁸⁰Sr at beam energies between 85 and 110 MeV. γ-γ coincidence measurements were performed with a thin target to investigate the level structure. Both neutron gated and singles angular distribution measurements were carried out to aid in the assignment of level spins. The directional correlation ratios extracted from the γ-γ coincidence data provided a consistency check for the spin assignments. Level lifetimes were measured by the Doppler shift attenuation method in a thick target γ-γ coincidence measurement. The ground state band has been identified up to (26⁺) and three previously unobserved sidebands have been discovered. The deduced level scheme is compared with cranking model calculations; the predicted transformation to mostly non-collective excitations of an oblate shape is not observed experimentally. The behaviour of the J⁽¹⁾ and J⁽²⁾ moments of inertia is discussed and presented as evidence for either static or dynamic γ-deformation in the light Sr isotopes. In addition, the level structure is compared with IBM-2 calculations. These calculations indicate the importance of proton excitations across the Z=40 subshell gap, into the g_9/2 orbital, and suggest that the lowest lying ⁸⁰Sr sideband can be identified with the collective IBM-2 quasi-γ band. NUCLEAR REACTIONS ⁵⁴Fe(²⁹Si, 2pn), ,em>E = 85 - 110 MeV; measured Eγ, Iγ(θ), γ-γ, n-γ coincidences, DCO ratios, Doppler shifted γ-ray lineshapes. ⁸⁰Sr deduced levels, J, π, τ. Enriched target, Ge(Li), Ge, NE213 detectors.

No description available.

No description available.

La structure nucléaire en couches évolue en allant vers des régions de plus en plus exotiques de la carte des noyaux, et par conséquent, les nombres magiques conventionnels (8, 20, 28, 50, 82, 126) peuvent disparaître loin de la stabilité, tandis que de nouveaux nombres magiques peuvent apparaître. Le noyau de ⁷⁸Ni, avec 28 protons et 50 neutrons, est un des noyaux supposés doublement magiques les plus exotiques et est donc d'un grand intérêt. L'évolution de la fermeture de couche à Z = 28 en allant vers N = 50 peut être étudiée en sondant le caractère de particule individuelle des niveaux dans la chaîne isotopique de cuivre, ayant un proton de plus que le nickel. Ce travail porte sur le ⁷⁹Cu, à N = 50. Afin d'effectuer la première spectroscopie gamma en ligne des noyaux autour du ⁷⁸Ni, une expérience a été réalisée à la Radioactive Ion Beam Factory du RIKEN, au Japon. Le noyau de ⁷⁹Cu était produit par la réaction de knockout (p,2p) à partir d'un faisceau de ⁸⁰Zn envoyé sur le dispositif MINOS, une cible d'hydrogène liquide couplée à une TPC servant à reconstruire la trajectoire des protons. L'émission de rayons gamma subséquente était détectée en vol par le scintillateur segmenté DALI2. Les spectromètres BigRIPS et ZeroDegree permettaient, respectivement, une identification sans ambiguïté des noyaux entrants et sortants.Une procédure d'analyse basée sur des coïncidences gamma-gamma a permis de construire le premier schéma de niveau du ⁷⁹Cu, avec des états jusqu'à 4.6 MeV, et les résultats ont été comparés à des calculs de modèle en couches Monte Carlo. Les conclusions montrent que le noyau de ⁷⁹Cu est bien décrit en termes d'un proton de valence en dehors d'un cœur fermé de ⁷⁸Ni, ce qui implique le caractère magique de ce dernier. / The nuclear shell structure is evolving when going into more and more exotic regions of the chart of isotopes and consequently, the conventional magic numbers (8, 20, 28, 50, 82, 126) may disappear far from stability, while some new magic numbers can appear. The ⁷⁸Ni nucleus, with its 28 protons and 50 neutrons, is one of the most exotic supposedly doubly-magic nuclei, making it of great interest. The evolution of the Z = 28 gap towards N = 50 can be studied by probing the single-particle character of the states in the copper isotopic chain, having one proton more than nickel. This work focuses on Cu, at N = 50.In the aim of performing the first in-beam gamma-ray spectroscopy of nuclei in the close vicinity of ⁷⁸Ni, an experiment was carried out at the Radioactive Isotope Beam Factory of RIKEN, in Japan. The ⁷⁹Cu nucleus was produced through the (p,2p) knockout reaction from a ⁸⁰Zn beam sent on the MINOS device, a liquid-hydrogen target coupled to a TPC used for proton tracking. The subsequent gamma-decay was detected in-beam with the DALI2 scintillator array. The BigRIPS and ZeroDegree spectrometers allowed an unambiguous identification of the incoming and outgoing nuclei, respectively.An analysis procedure based on gamma-gamma coincidences permitted to build the first level scheme of ⁷⁹Cu, with levels up to 4.6 MeV, and the results were compared to Monte-Carlo shell-model calculations for interpretation. The conclusions show that the ⁷⁹Cu nucleus is well described in terms of a valence proton outside a closed ⁷⁸Ni core, implying the magic character of the latter.

The nucleus is a mesoscopic system that retains features from both the quantum and macroscopic worlds. A basic property of a macroscopic body is its shape. Nuclear shapes can be deduced from experimental data as they influence the excitation mode of the nucleus and hence the energies and lifetimes of its excited levels. Various short-lived nuclei were created in fusion-evaporation experiments performed at international heavy-ion accelerator facilities. The emitted γ rays and, in some experiments, also the charged particles and neutrons emitted in the reactions were detected. The studied neutron-deficient isotopes were either selected by the type and number of particles emitted in the reactions, or by using their characteristic decays. The excited states of the different isotopes were extracted from the γ-ray analyses. Spectroscopic properties, such as the lifetimes of the excited states or the angular distribution of the emitted γ rays were measured when possible. The experimentally obtained level schemes together with the other spectroscopic information were used to deduce the excitation modes and the shapes of the studied nuclei. The detector systems are described in the first chapter and in the second chapter some techniques used to extract information from the experimental data are explained. Finally, a brief theoretical overview on the nuclear models which were used to interpret the experimental results is given. / QC 20100621