NEW ISOMER IN Y-80

The beta(+)/EC decay of mass-separated A = 80 nuclei was studied by me ans of beta- and gamma-ray spectroscopy after the bombardment of a Mg- 24 target with Ni-58 ions at 190 MeV. A new 1(-) isomer at 228.5(1) ke V has been identified in Y-80 With a half-life of 4.7(3) s. This new i somer decays to the 4(-) ground state with an 81(2)% branch and by bet a(+)/EC transitions to levels in Sr-80 With a 19(2)% branch. The half- life of the Y-80 ground-state decay has been remeasured to be 30.1(5) s. A level scheme for the low-lying stales in Y-80 is presented. Hartr ee-Fock-Bogolyubov calculations show a large prolate deformation for t hese states, and two-quasiparticle + rotor model calculation results s uggest that the low-lying states can be reproduced by inclusion of an effective proton-neutron residual interaction. The dominating Nilsson configurations for the 4(-) ground state and the 1(-) isomeric state h ave been found to originate from the parallel and antiparallel couplin g of the proton [422]5/2(+) and the neutron [301]3/2(-) orbitals.