2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/142519For a core plus one neutron system like 11Be we have calculated the energies of the 1/2- and 1/2+ states assuming a deformation of the core deduced from the low energy 2+ state properties or taking into account the coupling of the neutron with this 2+ state interpreted as a spherical one-phonon state. We have shown that the two derivations yield identical results if the phonon energy is neglected in the second derivation and close results in the general case.Nuclear Theorytext