Excited states in 20O were populated in the reaction 10Be(14C,α) at Florida State University. Charged particles were detected with a particle telescope consisting of 4 annularly segmented Si surface barrier detectors and γ radiation was detected with the FSU γ detector array. Five new states were observed below 6 MeV from the α-γ and α-γ-γ coincidence data. Shell model calculations suggest that most of the newly observed states are core-excited 1p-1h excitations across the N=Z=8 shell gap. Comparisons between experimental data and calculations for the neutron-rich O and F isotopes imply a steady reduction of the p-sd shell gap as neutrons are added.
@article{arxiv.nucl-ex/0412028,
title = {$p$-$sd$ shell gap reduction in neutron-rich systems and cross-shell excitations in $^{20}$O},
author = {M. Wiedeking and S. L. Tabor and J. Pavan and A. Volya and A. L. Aguilar and I. J. Calderin and D. B. Campbell and W. T. Cluff and E. Diffenderfer and J. Fridmann and C. R. Hoffman and K. W. Kemper and S. Lee and M. A. Riley and B. T. Roeder and C. Teal and V. Tripathi and I. Wiedenhöver},
journal= {arXiv preprint arXiv:nucl-ex/0412028},
year = {2009}
}