Spectroscopy of odd-mass cobalt isotopes toward the N=40 subshell closure and shell-model description of spherical and deformed states

The neutron-rich cobalt isotopes up to A = 67 have been studied through multinucleon transfer reactions by bombarding a 238U target with a 460-MeV 70Zn beam. Unambiguous identification of prompt γ rays belonging to each nucleus has been achieved using coincidence relationships with the ions detected in a high-acceptance magnetic spectrometer. The new data are discussed in terms of the systematics of the cobalt isotopes and interpreted with large-scale shell-model calculations in the fpgd model space. In particular, very different shapes can be described in 67Co, at the edge of the island of inversion at N = 40, where a low-lying highly deformed band coexists with a spherical structure
This work was partially supported by the European Community FP6, Structuring the ERA Integrated Infrastructure Initiative Contract No. EURONS RII3-CT-2004-506065, by MICINN, Spain (Contract No. FPA2011-29854), by IN2P3, France (Contract No. AIC-D-2011-648), by Comunidad de Madrid, Spain (Contract No. HEPHACOS S2009-ESP-1473), and by Generalitat Valenciana, Spain (Contract No. PROMETEO/ 2010/101). A. Gadea and E. Farnea acknowledge the support of MICINN, Spain, and INFN, Italy, through the AIC-D-2011-0746 bilateral action