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Etude de la Structure des Noyaux Riches en Neutrons autour du Noyau Doublement Magique 78Ni

Abstract : In the last decade, $\beta$-decay studies in $^{69, 71, 73}$Cu isotopes have evidenced the sharp lowering of the $\pi 1f_{5/2}$ orbital as the occupancy of the $\nu 1g_{9/2}$ orbital increases. This phenomenon can be interpreted as the result of the tensor forces between these proton and neuron orbitals. With a similar argument, a weakening of the N=50 shell gap when approaching the $^{78}$Ni nucleus is predicted due to the attraction between the $\nu 1g_{9/2}$ and $\nu 1d_{5/2}$ configurations with the $\pi 1f_{5/2}$ state and the repulsion between the $\nu 1g_{7/2}$ with the $\pi 1f_{5/2}$ state. Nuclei in the viciniy of the doubly-magic $^{78}$Ni nucleus are amongst the best candidates to study the N=50 shell-closure evolution and other aspects of shell model at large N/Z ratio. Such studies can be addressed by the use of powerful experimental setups like the combination of a large acceptance mass spectrometer coupled to a large granularity $\gamma$-ray detector array such as PRISMA and CLARA at LNL, Legnaro (Italy). The latter setup enables systematic studies of the structure of a wide A and Z domain of neutron-rich nuclei around N=50. In a recent experiment the exotic residues were produced via deep-inelastic reactions between a $^{82}$Se beam ($E_{lab}=505$ MeV) and an uranium target. Quasi-projectile yrast states are principally populated with $I < 10 \hbar$ in the isotopic chains $24 \leq Z \leq 36$ ($^{74-82}$Ge, $^{72-77}$Zn, $^{61-69}$Co for example). In order to complete these $\gamma$-spectroscopy data, obtained at Legnaro, the $\beta$-decay of neutron-rich copper isotopes has also been studied. These experiments performed at the ISOLDE facility at CERN (Geneva, Switzerland) feed low spin yrare states, accordingly to decay rules. Preliminary partial level schemes of odd zinc isotopes (A=73,75,77) have been built, for the first time for the most exotic ones ($^{75,77}$Zn). The complementarity of these two reaction mechanisms opens new perspectives for the study of exotic nuclei.
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Tatjana Faul. Etude de la Structure des Noyaux Riches en Neutrons autour du Noyau Doublement Magique 78Ni. Physique Nucléaire Théorique [nucl-th]. Université Louis Pasteur - Strasbourg I, 2007. Français. ⟨tel-00610309⟩

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