Evidence for core excitation in single-particle states of 19Na

We present an experimental study of 19Na states in the excitation energy range between 2 and 3 MeV. The presence of 19Na single-particle levels at these energies was first predicted by a microscopic cluster model and then experimentally confirmed by measuring the elastic and inelastic scattering of a 66 MeV 18Ne radioactive beam on a (CH2)n target. The H(18Ne, p)18Ne(g.s.) and H(18Ne, p′)18Ne*(2+,1.887MeV) cross sections have been obtained in the laboratory angular range θlab=6.1°-18.4° and analyzed by using the R-matrix method. Two new states in 19Na have been observed at centre-of-mass energies Ec.m.=2.78±0.01MeV and 3.09±0.05MeV. Both resonances exhibit large widths in the Ne18(2+)+p channel, and low branching ratios into the elastic channel. The reduced proton widths confirm the single-particle nature of these states, with a Ne18(2+)+p structure.