p−sdShell Gap Reduction in Neutron-Rich Systems and Cross-Shell Excitations inO20
Physical Review Letters
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
... . 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.