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rapid onset of collectivity in the vicinity of 78Ni
Lebois Matthieu1, David Verney1, Fadi Ibrahim1, Said Essabaa1, Faiçal Azaiez1, Maher Cheikh Mhamed1, Evelyne Cottereau1, Cuong Phan Viet1, Mathieu Ferraton1, Kieran Flanagan1, Serge Franchoo1, Dominique Guillemaud Mueller1, Fairouz Hammache1, Christophe Lau1, François Le Blanc1, Jean François Le Du1, Baptiste Mouginot1, Costel Petrache1, Brigitte Roussière1, Lionel Sagui1, Nicolas De Sereville1, Iulian Stefan1, Benoit Tastet1
ALTO Collaboration(s)

gamma-rays following the β and β-n decay of the very neutron rich 84Ga produced by photo-fission of 238U have been studied at the newly built ISOL facility of IPN Orsay: ALTO. Two activities were observed and assigned to two β-decaying states: 84gGa, I = (0−) and 84mGa, I= (3−,4−). Excitation energies of the 2+1 and 4+1 excited states of 84Ge were measured at E(2+1 ) = 624.3 keV and E(4+1 ) = 1670.1 keV. Comparison with HFB+GCM calculations allows to establish the collective character of this nucleus indicating a substantial N=50 core polarization. The excitation energy of the 1/2+1 state in 83Ga known to carry a large part of the neutron 3s1/2 strength was measured at 247.8keV. Altogether these data allow to confirm the new single particle state ordering which appears immediately after the double Z=28 and N=50 shell closure and to designate 78Ni as a fragile and easily polarized doubly-magic core.
1 :  IPNO - Institut de Physique Nucléaire d'Orsay
Physique/Physique Nucléaire Expérimentale
structure nucléaire – N=50 – ALTO – 84Ga – 84Ge – 83Ge
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