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In this study, I-pi = 1(+) and I-pi = 1(-) dipole mode excitations are systematically investigated within the rotational and translational + Galilean invariant quasiparticle random-phase approximation for Th-232, U-236, and U-238 actinide nuclei. It is shown that the investigated nuclei reach a B(M1) strength structure, which corresponds to the scissors mode. The calculated mean excitation energies as well as the summed B(M1) value of the scissors mode excitations are consistent with the available experimental data. The results of calculations indicate large differences to the rare-earth nuclei as is the case for the experiment: a doubling of the observed dipole strengths and a shift of the energy centroid to the lower energies by about 800 keV. The calculations indicate the presence of a few prominent negative-parity K-pi = 1(-) states in the 2.0-4.0 MeV energy interval. The occurrence of the negative-parity dipole states with the rather high B(E1) value less than 4 MeV shows the necessity of explicit parity measurements for the correct determination of the scissors mode strength in Th-232, U-236, and U-238 isotopes.

In this study the QRPA approach with the rotational and translational invariant Hamiltonians has been carried out to describe magnetic and electric dipole excitations in 176Hf . Calculations show that the 176Hf nucleus demonstrates a very rich B(M1) strength structure and in some aspects nicely confirm the experimental data. It has been shown that the main part of spin-1 states, observed at 2-4MeV in 176Hf , may be attributed to have a M1 character and may be interpreted as the main fragments of the scissors mode. The agreement between the calculated mean excitation energies as well as the summed B(M1) values of the scissors mode excitations and the available experimental data is quite good. The constructive interference between the orbit and the spin part of M1 strength has been found to be below 3.5MeV. The calculations indicate the presence of a few prominent negative-parity $\ensuremath K^{\pi} = 1^{-}$ states in the 2-4MeV energy interval. This suggests that the supposition of the experiment “all stronger $ \Delta$ K = 1 low-lying dipole excitations were of magnetic character” cannot be generalized.