Cross-shell excitations from the f p shell: Lifetime measurements in Zn-61

Abstract

Lifetimes of excited states in the neutron-deficient nucleus 61Zn were measured employing the recoil-distance Doppler-shift (RDDS) and the electronic fast-timing methods at the University of Cologne. The nucleus of interest was populated as an evaporation residue in 40Ca(24Mg,n2p)61Zn and 58Ni(α,n)61Zn reactions at 67 and 19 MeV, respectively. Five lifetimes were measured for the first time, including the lifetime of the 5/2−1 isomer at 124 keV. Short lifetimes from the RDDS analysis are corrected for Doppler-shift attenuation (DSA) in the target and stopper foils. Ambiguous observations in previous measurements were resolved. The obtained lifetimes are compared to predictions from different sets of shell-model calculations in the fp, f5/2pg9/2, and multishell fp−g9/2d5/2 model spaces. The band built on the 9/2+1 state exhibits a prolate deformation with β≈0.24. Especially, the inclusion of cross-shell excitation into the 1d5/2 orbital is found to be decisive for the description of collectivity in the first excited positive-parity band.status: publishe