The exotic nuclei 11Be and 11N in a microscopic cluster model

The 11Be nucleus is investigated in the generator coordinate method, using 10Be+n microscopic wave functions. The 10Be wave functions are defined in the harmonic oscillator model with all p-shell configurations. The model confirms the halo structure of the 11Be ground state, and of its 1/2- first excited state. The former is suggested to have a dominant 10Be(g.s.)+n component, and the latter a dominant 10Be(2+)+n structure. We compute neutron and proton densities in both states, and the corresponding r.m.s. radii. Properties of unbound states are discussed. The theoretical photo-absorption cross section of 11Be presents a strong peak at low energies, which is interpreted as its soft dipole mode. The same model is applied to the mirror 11N nucleus, whose ground state is particle unstable. (orig.)