Quadrupole and other multipole excitations in skin nuclei

Quadrupole excitations are investigated theoretically in Sn nuclei at energies up to 35 MeV. A method incorporating the density functional theory (DFT) and quasiparticle-phonon model (QPM) is applied. A question of a special interest is to what extent the presence of a neutron or proton skin will affect low-energy 2+ states located above the 2+1 state and below the neutron threshold, particularly exploring their connection to the thickness of the neutron or proton skin, respectively. By analyzing of the structure and transition densities of the quadrupole states, a new quadrupole mode at excitation energies E*∼ 2-4 MeV is identified and related to pygmy quadrupole resonance (PQR). Furthermore, the unique character of the PQR states is confirmed in QPM calculations of M1 and E2 transitions indicating that these states are different from the known scissors mode which are typically located in similar energy domain. Investigations of electric and magnetic dipole strength distributions in skin nuclei at different mass regions are discussed and compared to experimental data. The results reveal interesting aspects of the nuclear isospin dynamics.