Nuclear structure of 18N and the neighboring N=11 isotones

The fusion-evaporation reaction 9Be(11B,2p) was used to populate excited states in 18N. New gamma-ray transitions were added to the 18N level scheme. The mean lifetime of the first excited state was measured to be 582(165) ps and its transition rate to the ground state was determined to be B(M1)=0.036(10) W.u. Shell model calculations in the full p-sd model space were used to investigate the low-lying configurations in 18N and in the N=11 isotones 17C and 19O. It was found that the role of the proton-neutron interaction is important in determining the ground state and low-lying excited state properties. The ground state spin inversion in these isotones is attributed to the increased importance of the quadrupole relative to the pairing interaction and is discussed within the framework of a schematic pairing + quadrupole model