New isomer in80Y

Abstract

The {beta}{sup +}/EC decay of mass-separated A=80 nuclei was studied by means of {beta}- and {gamma}-ray spectroscopy after the bombardment of a {sup 24}Mg target with {sup 58}Ni ions at 190 MeV. A new 1{sup {minus}} isomer at 228.5(1) keV has been identified in {sup 80}Y with a half-life of 4.7(3) s. This new isomer decays to the 4{sup {minus}} ground state with an 81(2){percent} branch and by {beta}{sup +}/EC transitions to levels in {sup 80}Sr with a 19(2){percent} branch. The half-life of the {sup 80}Y ground-state decay has been remeasured to be 30.1(5) s. A level scheme for the low-lying states in {sup 80}Y is presented. Hartree-Fock-Bogolyubov calculations show a large prolate deformation for these states, and two-quasiparticle + rotor model calculation results suggest that the low-lying states can be reproduced by inclusion of an effective proton-neutron residual interaction. The dominating Nilsson configurations for the 4{sup {minus}} ground state and the 1{sup {minus}} isomeric state have been found to originate from the parallel and antiparallel coupling of the proton [422]5/2{sup +} and the neutron [301]3/2{sup {minus}} orbitals. {copyright} {ital 1998} {ital The American Physical Society}