Spectroscopic study of neutron shell closures via nucleon transfer in the near-dripline nucleus 23O.
ABSTRACT Neutron single particle energies have been measured in 23O using the 22O(d,p)23O*-->22O+n process. The energies of the resonant states have been deduced to be 4.00(2) MeV and 5.30(4) MeV. The first excited state can be assigned to the nu d3/2 single particle state from a comparison with shell model calculations. The measured 4.0 MeV energy difference between the nu s1/2 and nu d3/2 states gives the size of the N=16 shell gap which is in agreement with the recent USD05 ("universal" sd from 2005) shell model calculation, and is large enough to explain the unbound nature of the oxygen isotopes heavier than A=24. The resonance detected at 5.3 MeV can be assigned to a state out of the sd shell model space. Its energy corresponds to a approximately 1.3 MeV sized N=20 shell gap, therefore, the N=20 shell closure disappears at Z=8 in agreement with Monte Carlo shell model calculations using SDPF-M interaction.
- [Show abstract] [Hide abstract]
ABSTRACT: The spectroscopy of O21 has been investigated using a radioactive O20 beam and the (d,p) reaction in inverse kinematics. The ground and first excited states have been determined to be Jpi=5/2+ and 1/2+, respectively. Two neutron unbound states were observed at excitation energies of 4.77(10) and 6.17(11) MeV. The spectroscopic factor deduced for the lower of these, interpreted as a 3/2+ level, reveals a relatively pure (60%) 0d3/2 single-particle configuration, in good agreement with shell-model calculations that predict O26 to be unbound. The large energy difference between the 3/2+ and 1/2+ states is indicative of the emergence of the N=16 shell gap, which is estimated to be 5.1(11) MeV. For the higher-lying resonance, which has a character consistent with a spin-parity assignment of 3/2+ or 7/2-, a 0.71(22) branching ratio to the first 2+ state in O20 has been observed.Physical Review C 01/2011; 84. · 3.88 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: The neutron-rich oxygen isotope 23O has been investigated via proton inelastic scattering on a liquid hydrogen target at 63.5 MeV/nucleon. The invariant mass method in inverse kinematics was employed to reconstruct the energy spectrum. A sharp resonance state was observed at 42(5) keV above the neutron threshold. A comparison of the differential cross section leading to this state with a microscopic DWBA calculation allowed a J π assignment of 5/2+ for this state.Few-Body Systems 01/2013; 54(1-4):287-290. · 1.51 Impact Factor
Article: Disappearance of the N= 14 shell[Show abstract] [Hide abstract]
ABSTRACT: An excited state of 22N unbound with respect to neutron emission was observed in a stripping reaction from a 85 MeV/nucleon 26F 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 22N, 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 22N, a disappearance of the gap and even a level inversion of the ν1s1/2 and the ν0d5/2 levels in the neutron-unbound nucleus 21C seems likely.Physical Review C 08/2009; 80(2). · 3.88 Impact Factor