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

Abstract

Recent experimental results obtained using $\beta$ 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

References in corpus (4)

• Configuration mixing of angular-momentum and particle-number projected triaxial HFB states using the Skyrme energy density functional
• Shell Structure of Exotic Nuclei
• Beyond the relativistic mean-field approximation (II): configuration mixing of mean-field wave functions projected on angular momentum and particle number
• Angular momentum projection of cranked Hartree-Fock states: Application to terminating bands in A~44 nuclei