Residual Interaction Effect on Isoscalar Dipole Modes in Heavy Nuclei
Isoscalar collective dipole excitations in heavy nuclei have been studied in the framework of the kinetic model for small vibrations in a finite Fermi system with a moving surface. An analytical expression for the second-order isoscalar response function of the dipole moment is obtained taking the residual interaction between nucleons into account in the separable approximation. It is shown that the inclusion of the residual interaction does not violate the translation invariance of the model. The strength function has a two-resonance structure, like in the zeroth-order approximation (i.e. neglecting the residual interaction). The account for the isoscalar dipole residual interaction decreases the compressibility of a system and shifts the resonances toward low frequencies, which improves the agreement with experimental data for both low- and high-energy isoscalar dipole modes in heavy nuclei.