  Using an isospin-dependent transport model, we have studied the isospin and
momentum relaxation times in the heavy residues formed in heavy-ion collisions
at intermediate energies. It is found that only at incident energies below the
Fermi energy, chemical or thermal equilibrium can be reached before dynamical
instability is developed in the heavy residues. Also, the isospin relaxation
time is shorter (longer) than that for momentum at beam energies lower (higher)
than the Fermi energy.
