On the origin of the anomalous behaviour of 2+ excitation energies in the neutron-rich Cd isotopes

Rodríguez, Tomás R.; Egido, J. Luis; Jungclaus, Andrea

On the origin of the anomalous behaviour of 2+ excitation energies in the neutron-rich Cd isotopes

Authors

Rodríguez, Tomás R.

Egido, J. Luis

Jungclaus, Andrea

Description

Recent experimental results obtained using $β$ decay and isomer spectroscopy indicate an unusual behaviour of the energies of the first excited 2$^{+}$ states in neutron-rich Cd isotopes approaching the N=82 shell closure. To explain the unexpected trend, changes of the nuclear structure far-off stability have been suggested, namely a quenching of the N=82 shell gap already in $^{130}$Cd, only two proton holes away from doubly magic $^{132}$Sn. We study the behaviour of the 2$^+$ energies in the Cd isotopes from N=50 to N=82, i.e. across the entire span of a major neutron shell using modern beyond mean field techniques and the Gogny force. We demonstrate that the observed low 2$^+$ excitation energy in $^{128}$Cd close to the N=82 shell closure is a consequence of the doubly magic character of this nucleus for oblate deformation favoring thereby prolate configurations rather than spherical ones.
10 pages, 4 figures, to be publised in Phys. Lett. B