Dissipation effect in nuclear collective motion

New derivation of motion equations is proposed for the macroscopic collective variable (the shape of the nucleus σ, for example), accounting for dissipation effects by means of special quantity-nuclear friction coefficient γ(σ). Relationship is obtained between the mass coefficient B(σ), nuclear friction coefficient γ(σ) and the intrinsic properties of a nucleus. Quantitative magnitudes for the collective-motion relaxation time are estimated for some simple nuclear models. Existence of the qualitative correlation between the shell oscillations and the nucleon-number dependence of the friction coefficient is established. Total energy dissipation is found. Nuclear temperature dependence on energy dissipation is complicated due to the shell effects. Single-particle character of the dissipation mechanism is preserved by internucleon interaction taken into account by the selfconsistent mean field. The collisional mechanism of dissipation appears only when correlational internucleon interaction is taken into account. The latter results in the particle-hole eicitation fragmentation in more complex nuclear states