Results of nuclear resonance fluorescence experiments on ${}^{117}\mathrm{Sn}$ are reported. More than 50 $\gamma$ transitions with $E_{\gamma }<4\mathrm{}\mathrm{MeV}$ 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 $E1\mathrm{}$ transitions are the strongest ones also $M1\mathrm{}$ and $E2\mathrm{}$ decays contribute substantially to the observed spectra. In contrast to the neighboring even ${}^{116–124}\mathrm{Sn}$ nuclei, in ${}^{117}\mathrm{Sn}$ the $1^{-}$ component of the two-phonon $[2_1^{+}\otimes 3_1^{-}]$ multiplet built on top of the ${1/2}^{+}$ ground state is proved to be fragmented.

• Received 4 June 1999

DOI:https://doi.org/10.1103/PhysRevLett.83.4029