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Séminaire présenté par Victor Modamio, INFN Legnaro, Italy

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Evolution of collectivity below N=40 68Ni

Par : Victor Modamio, INFN Legnaro, Italy
Date : vendredi 8 février 2013 à 10h30
Lieu : IPHC, Salle de Réunion 2e étage du Bâtiment 27

Résumé :

The medium-mass region around the neutron-rich Ni isotope 68Ni arouses many interest concerning the shell evolution. The sudden increase in excitation energy for the 2+ state as well as the occurrence of a low excited second 0+ indicates a shell closure at N=40. This restoration of the harmonic oscillator shell closure is driven by the weakness of the spin-orbit interaction when increasing the number of neutrons, preventing the intruder orbital g9/2 going down.

However, this shell gap have been shown to disappear by removing protons from the 68Ni. With the proton f7/2 shell not fully filled, it is predicted a quadrupole deformation due to the interaction of this protons with neutrons promoted to the sdg shell. That is the case for N=40 66Fe and 64Cr, where new region of deformation have been observed.

We studied the evolution of collectivity in the cobalt chain. With one proton less than the spherical nickels and deformed irons, Co isotopes shows coexisting states with both single particle and collective character. The multiplet with spins 9/2- and 11/2- in their low excitation spectra have been observed to follow the trend of the Ni 2+ excitation energies. Albeit reduced transition probabilities provides much more rich information about the collective character on this transitions.

For this purpose, lifetimes for the 11/2- excitation states in both 63Co and 65Co isotopes have been measured employing the Recoil-Distance-Doppler-Shift method. Experimental B(E2) values are compared with large-scale shell model calculations, leading us to draw some remarks on the role of the d5/2 and g9/2 neutron orbitals in driving collectivity by excitations above N=40.

Personne à contacter : Kamila SIEJA