Allowed-unhindered β decay of Yb180 and the nuclear structure of Lu180

The β decay of mass-separated Yb180 was investigated by measuring β-delayed γ rays and conversion electrons. Evidence was found for an allowed-unhindered β transition involving the transformation of a 7/2-[514] neutron into a 9/2-[514] proton. The experimental results include a new decay scheme of Yb180 which gives evidence for a 5+ ground state of Lu180 and leads to the first identification of further low-spin configurations. These data are compared with predictions obtained from two-quasiparticle band-head energy calculations based on a zero-range residual interaction with appropriate Nilsson model wave functions.