Selective population and neutron decay of the first excited state of   semi-magic O-23
  We have observed an excited state in the neutron-rich semi-magic nucleus O-23 for the first time. No such states have been found in previous searches using gamma-ray spectroscopy. The observation of a resonance in n-fragment coincidence measurements confirms the speculation in the literature that the lowest excited state is neutron unbound and establishes positive evidence for a 2.8(1) MeV excitation energy of the first excited state in O-23. The non-observation of a predicted second excited state is explained assuming selectivity of inner-shell knockout reactions. 
A. Schiller, N. Frank, T. Baumann, D. Bazin, B.A. Brown, J. Brown,   P.A. DeYoung, J.E. Finck, A. Gade, J. Hinnefeld, R. How...