  We consider a quasiclassical model that allows us to simulate the process of
spin diffusion and relaxation in the presence of a highly nonuniform magnetic
field. The energy of the slow relaxing spins flows to the fast relaxing spins
due to the dipole-dipole interaction between the spins. The magnetic field
gradient suppresses spin diffusion and increases the overall relaxation time in
the system. The results of our numerical simulations are in a good agreement
with the available experimental data.
