Dipole Excitations in Deformed Nuclei

A study of magnetic and electric dipole excitations is carried out within the quasiparticle-phonon nuclear model with wave functions consisting of one- and two-phonon terms and in the random phase approximation for the deformed nuclei (154)Sm, (166)Er, (172,174)Yb, (178)Hf. and (238)U. It is shown that the computed MI strength below 4 MeV is much more strongly fragmented than in Gd and Dy isotopes. The calculated M1 and E1 strengths summed in the energy range 2-4 MeV are in agreement with the relevant experimental data. It is found that the orbital motion, although giving on the whole a modest contribution to the M1 strength, plays a significant role in shaping the M1 spectra because of the destructive interference between orbital and spin amplitudes. Strong £1 transitions also occur in the same energy range. Their total strength in the energy range 3.6-7.6 MeV is about 4 times larger than the M1 strength. Because of these highly intense £1 transitions, the total dipole strength distribution computed as a sum of the M\ and £1 strengths is considerably different from the spectra of the M\ transitions alone.