Onset of large deformation and the occurrence of anomalous high-spin yrast spectra in the zirconium region.

Abstract

The observed dramatic onset of large deformations in the highly neutron-rich Zr and Mo isotopes is examined by carrying out self-consistent Hartree-Fock-Bogoliubov calculations employing pairing-plus-quadrupole-quadrupole effective interactions operating in a reasonably large valence space outside an inert core. It turns out that the observed deformation systematics can be understood in terms of the polarization of the (2${d}_{5/2}$${)}^{6}$ part of the N=56 core initiated by the involvement of the 1${h}_{11/2}$ orbit in the underlying valence space. A variational calculation of the high-spin yrast spectra in the highly neutron-rich Mo isotopes suggests strongly the possibility of observing the backbending effect. It is also shown that the B(E2) values associated with the yrast spectra can provide unambiguous signatures of the large structural changes that are likely to occur in the high-spin yrast spectra of the nuclei in this new island of deformation.