Nuclear resonance fluorescence experiments were performed on the rare earth nuclei ${}_{}{}^{155}{}_{}{}^{}\mathrm{Gd}$ and ${}_{}{}^{159}{}_{}{}^{}\mathrm{Tb}$ to study the fragmentation of the M1 scissors mode in odd deformed nuclei and to establish a kind of systematics. Using the bremsstrahlung photon beam of the Stuttgart Dynamitron (end point energy 4.1 MeV) and high resolution Ge-γ spectrometers detailed information was obtained on excitation energies, decay widths, transition probabilities, and branching ratios. The results are compared to those observed recently for the neighboring odd nuclei ${}_{}{}^{161,163}{}_{}{}^{}\mathrm{Dy}$ and ${}_{}{}^{157}{}_{}{}^{}\mathrm{Gd}$. Whereas in the odd Dy isotopes the dipole strength is rather concentrated, both Gd isotopes show a strong fragmentation of the strength into about 25 ${(}^{155}$Gd) and 90 transitions ${(}^{157}$Gd) in the energy range 2–4 MeV. The nucleus ${}_{}{}^{159}{}_{}{}^{}\mathrm{Tb}$ linking the odd Dy and Gd isotopes exhibits an intermediate strength fragmentation. In general the observed total strength in the odd nuclei is reduced by a factor of 2–3 as compared to their neighboring even-even isotopes. The different fragmentation behavior of the dipole strengths in the odd Dy and Gd isotopes is unexplained up to now. © 1996 The American Physical Society.

• Received 18 June 1996

DOI:https://doi.org/10.1103/PhysRevC.54.2287