Quadrupole Vibrations in the Nickel Region: Structure of Odd-Mass Co Isotopes

The odd-mass cobalt nuclei from ${}_{}{}^{57}{}_{}{}^{}\mathrm{Co}$ to ${}_{}{}^{63}{}_{}{}^{}\mathrm{Co}$ are described in the framework of the unified model. The vibrational description of even-mass nickel isotopes is discussed and the $1{f_{\frac{7}{2}}}^{-1\mathrm{}}$, $1{f_{\frac{7}{2}}}^{-2\mathrm{}}\mathrm{}\left(0\right)2p_{\frac{3}{2}}$, $1{f_{\frac{7}{2}}}^{-2\mathrm{}}\mathrm{}\left(0\right)1f_{\frac{5}{2}}$, and $1{f_{\frac{7}{2}}}^{-2\mathrm{}}\mathrm{}\left(0\right)2p_{\frac{1}{2}}$ proton configurations are coupled to quadrupole vibrational cores. The spacings among these configurations are determined from stripping reaction data and from and analysis of binding energies, and the collective parameters are determined from experimental data on the Ni cores. Good general agreement of calculated and experimental properties is obtained without free parameters involved. For the best known isotopes, ${}_{}{}^{57}{}_{}{}^{}\mathrm{Co}$ and ${}_{}{}^{59}{}_{}{}^{}\mathrm{Co}$, a one-to-one correspondence of the eight or ten first calculated and experimental states is established. Observed spectroscopic factors in pickup and stripping reactions and electromagnetic properties are qualitatively well reproduced for the low-lying levels in general. For the available data most of the calculated values lie within 50% of the experimental values. On the basis of this agreement some spin and parity assignments are proposed among those compatible with experimental data. The results of other models are also discussed.