Spectroscopy of ⁷⁴Ge: From soft to rigid triaxiality

The first heavy ion fusion-evaporation reaction study for ⁷⁴Ge has been performed through the reaction channel Zn70(Li7,2np)Ge74 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 ^72,76Ge isotopes, an intermediate pattern of energy staggering S(I) is observed in the γ band of ⁷⁴Ge. The collective structure of ⁷⁴Ge, 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 ^72,76,78Ge 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 ⁷⁴Ge is revealed and ⁷⁴Ge is found to be the crucial nucleus marking the triaxial evolution from soft to rigid in Ge isotopes.