Dipole excitations in deformed nuclei

A study of magnetic and electric dipole excitations is carried out within t he quasiparticle-phonon nuclear model with wave functions consisting of one - and two-phonon terms and in the random phase approximation for the deform ed nuclei Sm-154, Er-166,Er-168, Yb-172,Yb-174, Hf-178, and U-238. It is sh own that the computed M1 strength below 4 MeV is much more strongly fragmen ted than in Gd and Dy isotopes. The calculated M1 and E1 strengths summed i n 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 m odest 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 E1 transitions also occur in the same energy range. Their total strength in the energy range 3.6-7.6 MeV is about 4 times larg er than the M1 strength. Because of these highly intense E1 transitions, th e total dipole strength distribution computed as a sum of the M1 and E1 str engths is considerably different from the spectra of the M1 transitions alo ne.