Masses and beta-Decay Spectroscopy of Neutron-Rich Odd-Odd Eu-160,Eu- 162 Nuclei: Evidence for a Subshell Gap with Large Deformation at N=98

The structure of deformed neutron-rich nuclei in the rare-earth region is of significant interest for both the astrophysics and nuclear structure fields. At present, a complete explanation for the observed peak in the elemental abundances at A∼160 eludes astrophysicists, and models depend on accurate quantities, such as masses, lifetimes, and branching ratios of deformed neutron-rich nuclei in this region. Unusual nuclear structure effects are also observed, such as the unexpectedly low energies of the first 2^+ levels in some even-even nuclei at N=98. In order to address these issues, mass and β-decay spectroscopy measurements of the ^160Eu_97 and ^162Eu_99 nuclei were performed at the Californium Rare Isotope Breeder Upgrade radioactive beam facility at Argonne National Laboratory. Evidence for a gap in the single-particle neutron energies at N=98 and for large deformation (β_2∼0.3) is discussed in relation to the unusual phenomena observed at this neutron number.