First Observation of the Scissors Mode in aγ-Soft Nucleus: The Case of196Pt

A nuclear resonance fluorescence experiment with one of the newly developed highly efficient EUROBALL cluster detectors has been performed on the $\gamma$-soft nucleus ${}^{196}\mathrm{Pt}$. Magnetic dipole excitations were observed between 2 and 3.5 MeV excitation energy. They are interpreted as the main fragments of the scissors mode based on the measured excitation strengths and branching ratios. A strong $\gamma$ decay, which we believe to be an $E2\mathrm{}$ decay of the scissors mode to the $2_1^{+}$ state, is observed. It allows an extraction of the effective boson quadrupole charges in the interacting boson model.