Disappearance of the N=14 shell gap in the carbon isotopic chain

Abstract

The structure of 617-20C nuclei was investigated by means of the in-beam γ-ray spectroscopy technique using fragmentation reactions of radioactive beams. Based on particle-γ and particle-γγ coincidence data, level schemes are constructed for the neutron-rich C17-20 nuclei. The systematics of the first excited 2+ states in the carbon isotopes is extended for the first time to A=20 showing that in contrast to the case of the oxygen isotopes, the N=14 subshell closure disappears. Experimental results are compared with shell-model calculations. Agreement between them is found only if a reduced neutron-neutron effective interaction is used. Implications of this reduced interaction in some properties of weakly bound neutron-rich Carbon are discussed. © 2008 The American Physical Society.