Disappearance of the N=14 Shell
An excited state of (22)N unbound with respect to neutron emission was observed in a stripping reaction from a 85 MeV/nucleon (26)F beam. The observed decay energy of 650(50) keV places the level, which is interpreted to be the first 3(-) state, at an excitation energy of 1.93(22) MeV. Together with the previously measured bound states of (22)N, reduction of the N=14 shell gap compared to less neutron-rich nitrogen isotopes at the neutron dripline is observed. Based on the magnitude of the reduction of the shell gap for (22)N, a disappearance of the gap and even a level inversion of the nu 1s(1/2) and the nu 0d(5/2) levels in the neutron-unbound nucleus (21)C seems likely.
Published in: Phys. Rev. C80, January 1, 2009, pages 021302(R)-. Copyright © 2009 American Physical Society. The final published version is available at: http://dx.doi.org/10.1103/PhysRevC.80.021302