Nuclear Structure around the N=16 subshell closure.

In-beam gamma-spectroscopy using fragmentation reactions of both stable and radioactive beams have been performed in order to study the structure of excited states in the neutron-rich 18,20C, 21–24O and 23,25F isotopes. For the produced fragments, γ-ray energies, intensities and γγ coincidences have been measured. Based on this information new level schemes are proposed up to the neutron separation energy for some of these isotopes. The systematics of the 2+ energy has been extended up to 20C in the C isotopic chain. Level schemes are suggested for 21O and 22O. The non observation of any γ-ray from 23O and 24O suggests that their excited states lie above the neutron decay thresholds. The study of F isotopes provides hint of the possible change in nuclear structure between the F and O isotopic chains. These results, together with the size of the N=14 and N=16 shell gaps in C,O,F isotopes are discussed in the framework of shell model calculations. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]