The spectroscopy of 21O has been investigated using a radioactive 20O beam and the (d,p) reaction in inverse kinematics. The ground and first excited states have been determined to be Jpi=5/2+ and Jpi=1/2+ respectively. Two neutron unbound states were observed at excitation energies of 4.76 +- 0.10 and 6.16 +- 0.11. The spectroscopic factor deduced for the lower of these interpreted as a 3/2+ level, reveals a rather pure 0d3/2 single-particle configuration. The large energy difference between the 3/2+ and 1/2+ states is indicative of the emergence of the N=16 magic number. For the higher lying resonance, which has a character consistent with a spin-parity assignment of 3/2+ or 7/2-, a 71% branching ratio to the first 2+ state in 20O has been observed. The results are compared with new shell model calculations.
@article{arxiv.1012.4040,
title = {Emergence of the N=16 shell gap in 21O},
author = {B. Fernandez-Dominguez and J. S. Thomas and W. N. Catford and F. Delaunay and S. M. Brown and N. A. Orr and M. Rejmund and N. L. Achouri and H. Al Falou and N. A. Ashwood and D. Beaumel and Y. Blumenfeld and B. A. Brown and R. Chapman and M. Chartier and N. Curtis and C. Force and G. de France and S. Franchoo and J. Guillot and P. Haigh and F. Hammache and M. Labiche and V. Lapoux and R. C. Lemmon and F. Marechal and A. Moro and B. Martin and X. Mougeot and B. Mouginot and L. Nalpas and A. Navin and N. Patterson and B. Pietras and E. C. Pollacco and A. Leprince and A. Ramus and J. A. Scarpaci and N. de Séréville and I. Stefan and O. Sorlin and G. Wilson},
journal= {arXiv preprint arXiv:1012.4040},
year = {2011}
}