Spectroscopy of neutron-rich nickel isotopes: Experimental results and microscopic interpretation

The spectroscopy of neutron-rich isotopes of ⁶⁷Ni and ⁶⁸Ni is studied using the quasi-elastic transfer reactions (¹⁴C,¹⁶O) and (¹⁴C,¹⁷O) on a ⁷⁰Zn mass separated target. The structure of these exotic nuclei is investigated in the framework of a microscopic collective model based on the Hartree-Fock-Bogoliubov theory. Gogny's two-body effective interaction is used. Collective excited states of ⁶⁸Ni are obtained by solving the Bohr Hamiltonian in which inertia parameters are calculated in the cranking approximation. Spin and parity assignments to observed excited levels are suggested on the basis of information deduced from this analysis. This assignment is further checked by comparing measured angular distributions to predictions. Predictions of the level structure of ⁷⁰Ni and ⁷⁸Ni isotopes are given. A more precise test of the 0⁺ wave functions is provided by the calculation of monopole operator of the 0₁⁺{→}0₂⁺ transition in ⁶⁸Ni. An impressive agreement is obtained between the measured and calculated half-life.