  Finite size effects in the equilibrium phase space density distribution
function are taken into account for alculations of the relaxation of collective
motion in finite nuclei. Memory effects in the collision integral and the
diffusivity and the quantum oscillations of the equilibrium distribution
function in momentum space are considered. It is shown that a smooth diffuse
(Fermi-type) equilibrium distribution function leads to a spurious contribution
to the relaxation time. The residual quantum oscillations of the equilibrium
distribution function eliminates the spurious contribution. It ensures the
disappearance of the gain and loss terms in the collision integral in the
ground state of the system and strongly reduces the internal collisional width
of the isoscalar giant quadrupole resonances.
