Gamma-decay of the 27/2− 0. 6s E3-isomer in 68 151 Er83

The nucleus 151Er was investigated through γ-ray and conversion electron measurements from its 27/2− isomer decay produced in a HI reaction at the GSI on-line mass separator. Inaddition tothe known intense yrast cascade,a complex 8% decay branch to above-yrast states was identified. Among these, the 11/2+ member of the νf7/2 × 3− septet was unambiguously characterised. Its energy implies that the quadrupole moment of the 3− core has changed sign with respect to the lighter even-Z N=83 isotones.