Systematic study of electric quadrupole excitations in the stable even mass Sn nuclei - art. no. 024309

The spherical semimagic Sn-116,Sn-118,Sn-120,Sn-122,Sn-124 nuclei have been investigated intensively using nuclear resonance fluorescence techniques. The measurement of the photon scattering cross sections, angular distributi ons, and Linear polarization or azimuthal asymmetries of the resonantly sca ttered (unpolarized and polarized) photons enabled a model independent dete rmination of reduced transition probabilities, level spins, and parities. B esides the enhanced dipole excitations to the well-known (2(1)(+) x 3(1)(-) )(1-) two-phonon states several electric quadrupole transitions were detect ed in the investigated energy region below 4 MeV. Quasiparticle phonon mode l calculations reveal several collective and noncollective 2(+) states in t his energy region. In contrast to the known two-phonon (2(1)(+) x 3(1)(-))( 1-) states, the wave functions of the observed 2(+) states are dominated by one-phonon components. However, the fragmentation of the B(E2) up arrow st rength is influenced by two-phonon 2(+) admixtures.