  The nonlinear evolution equation for the scattering amplitude of colour
dipole off the heavy nucleus is solved in the double logarithmic approximation.
It is found that if the initial parton density in a nucleus is smaller then
some critical value, then the scattering amplitude is a function of one scaling
variable inside the saturation region, whereas if it is greater then the
critical value, then the scaling behaviour breaks down. Dependence of the
saturation scale on the number of nucleons is discussed as well.
