T=52 27Na from 14C+14C, and the N=16 shell gap

For the first time a comprehensive level and decay scheme has been obtained for a T = 5/2 nucleus in the s-d shell (Na-27) by using a radioactive beam and target. Particle-gamma and p-gamma-gamma coincidences were measured following the C-14(C-14,pgamma)Na-27 reaction at E-lab = 22 MeV. The results do not support an inversion of the 2s(1/2) and 1d(5/2) orbitals, as previously proposed for T(z)greater than or equal to3, but they do suggest an increased N = 16 gap between the 2s(1/2) and 1d(3/2) orbitals due to the neutron excess. A consistent interpretation of the level scheme in terms of the s-d shell model using the USD Hamiltonian is possible below 4 MeV, but differences increase at higher excitation energies. Another interpretation is that the influences of both the p(1/2) and f(7/2) intruder orbitals increase simultaneously with increasing T, an effect not included in the USD Hamiltonian.