Missing mass spectroscopy on oxygen isotopes beyond the proton-drip line: mirror symmetry of nuclear shell evolution
Institut de Physique Nucléaire (IPN), IN2P3-CNRS, Université de Paris-Sud, F-91406, Orsay, France
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Revised: 3 September 2012
Accepted: 9 September 2012
Published online: 28 September 2012
Missing mass spectroscopy of the proton-rich 12O and 13O nuclei was performed via the neutron transfer (p, t and (p, d reactions, respectively, using a 14O beam of 51 MeV/u at GANIL (Grand Accélérateur National d’Ions Lourds). In addition to the ground states, an excited state of 12O at 1.8(4) MeV and two excited states of 13O at 2.8(3) and 4.2(3) MeV were observed. Spin-parity and/or spectroscopic factors were obtained from the comparison of the differential cross-sections to distorted-wave calculations. The excited state of 12O with a suggested spin-parity of 0+ or 2+ has a significantly low excitation energy, indicating that the proton shell closure at Z = 8 vanishes in 12O. The spin-parity of 1/2+ was suggested for the 2.8MeV state, which implies that the proton shell gap is weak in 13O, whereas the large spectroscopic factor extracted from the 14O(p , d reaction indicates that the ground 3/2− state remains dominated by normal p-shell configurations. These features of 12O and 13O have marked similarities with their neutron-rich mirror partners 12Be and 13B, respectively, demonstrating mirror symmetry in the fading of the shell closure at magic numbers 8 near the drip lines.
© SIF, Springer-Verlag Berlin Heidelberg, 2012