Strong Fragmentation of Low-Energy Electromagnetic Excitation Strength in 117 Sn

Results of nuclear resonance fluorescence experiments on Sn-117 are reported. More than 50 gamma transitions with E gamma < 4 MeV were detected. For the first time microscopic calculations making use of a complete configuration space for low-lying states are performed for a heavy odd-mass spherical nucleus. The theoretical predictions are in good agreement with the data. It is concluded that although the El transitions are the strongest ones also M1 and E2 decays contribute substantially to the observed spectra. In contrast to the neighboring even Sn116-124 nuclei, in Sn-117 the 1(-) component of the two-phonon [2(1)(+) x 3(1)(-)] multiplet built on top of the 1/2(+) ground state is proved to be fragmented.