Search for the electric dipole excitations to the 3s1/2⊗[21+⊗31-] multiplet in 117Sn

The odd-mass Sn-117 nucleus was investigated in nuclear resonance fluorescence experiments up to an end point energy of the incident photon spectrum of 4.1 MeV at the bremsstrahlung facility of the Stuttgart University. More than 50 mainly hitherto unknown levels were found. From the measurement of the scattering cross sections model independent absolute excitation strengths were extracted. The measured angular distributions suggested the spins of 11 excited levels. Quasiparticle phonon model calculations including a complete configuration space were performed for the first time for a heavy odd-mass spherical nucleus. These calculations give a clear insight in the fragmentation and distribution of the E1, M1, and E2 excitation strength in the low energy region. It is proven that the 1(-) component of the two-phonon [2(1)(+) x 3(1)(-)] quintuplet built on top of the 1/2(+) ground state is strongly fragmented. The theoretical calculations are consistent with the experimental data.