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

The Be-11 nucleus is investigated in the Generator Coordinate Method, using Be-10+n microscopic wave functions. The Be-10 wave functions are defined in the harmonic oscillator model with all p-shell configurations. The model confirms the halo structure of the Be-11 ground state, and of its 1/2(-) first excited state. The former is suggested to have a dominant Be-10(g.s.)+n component, and the latter a dominant Be-10(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 Be-11 presents a strong peak at low energies, which is interpreted as its soft dipole mode. The same model is applied to the mirror N-11 nucleus, whose ground state is particle unstable. (C) 1997 Elsevier Science B.V.