Unexpected properties of the scissors mode in the odd-mass nucleus 167Er

We report a study of the 167Er(γ, γ′) reaction in the excitation energy range Ex = 1.9–4.3 MeV. The total magnetic dipole strength above 2.5 MeV attributed to the scissors mode amounts to B(M1)↑=3.14(1.12) μn2, much larger than all values previously reported for odd-A nuclei, but fitting well into the systematics in the rare-earth region. In the region Ex > 3.9 MeV not accessed in previous experiments appreciable M1 strength is found indicating a spreading of the scissors mode over a large energy interval of about 2 MeV. The data can be described quantitatively by an interacting boson-fermion model calculation using boson g-factors gπ(gν) = 1(0) μn.