Eur. Phys. J. A (2012) 48: 130
https://doi.org/10.1140/epja/i2012-12130-6

Review

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

^* e-mail: suzuki@ipno.in2p3.fr

Received: 4 July 2012
Revised: 3 September 2012
Accepted: 9 September 2012
Published online: 28 September 2012

Abstract

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.