Spectroscopy of 74Ge: From soft to rigid triaxiality

Abstract The first heavy ion fusion–evaporation reaction study for 74 Ge has been performed through the reaction channel Zn 70 ( Li 7 , 2 n p ) Ge 74 at beam energies of 30 and 35 MeV. Previously known yrast band is extended to higher spins and five new collective bands are established. Based on comparison with the neighboring 72,76 Ge isotopes, an intermediate pattern of energy staggering S ( I ) is observed in the γ band of 74 Ge. The collective structure of 74 Ge, including the excitation energies and transition probabilities of ground-state band and γ band, is reproduced by the state-of-the-art five-dimensional collective Hamiltonian (5DCH) model constructed from the covariant density functional. By including the 72,76,78 Ge isotopes, systematical investigation of the structure evolution in Ge isotopes is performed. Based on the systematic comparisons and analysis, the triaxial evolution with spin in 74 Ge is revealed and 74 Ge is found to be the crucial nucleus marking the triaxial evolution from soft to rigid in Ge isotopes.