Toroidal, compression, and vortical dipole strengths in 144-154Sm: Skyrme-RPA exploration of the deformation effect

A comparative analysis of toroidal, compressional and vortical dipole strengths in the spherical Sm-144 and the deformed Sm-154 is performed within the random-phase approximation using a set of different Skyrme forces. Isoscalar (T = 0), isovector (T = 1), and electromagnetic excitation channels are considered. The role of the nuclear convection j(con) and magnetization j(mag) currents is inspected. It is shown that the deformation leads to an appreciable redistribution of the strengths and causes a spectacular deformation splitting (exceeding 5 MeV) of the isoscalar compressional mode. When stepping from Sm-144 to Sm-154, we observe an increase of the toroidal, compression and vortical contributions in the low-energy region (often called pygmy resonance). The strength in this region seems to be an overlap of various excitation modes. The energy centroids of the strengths depend significantly on the isoscalar effective mass m(0). Skyrme forces with a large m(0) (typically m(0)/m approximate to 0.8-1) seem to be more suitable for the description of experimental data for the isoscalar giant dipole resonance.