The formation of colloids in alkali halides, due to ionizing radiation, was studied by means of the Monte Carlo simulation of the aggregation of F centers. This involved a 2-dimensional lattice-gas Ising model which was defined by a Hamiltonian that described a thermally driven transition from a gas (F centers) to a solid (condensed colloids). In addition, 2 mechanisms which were specific to the irradiation of alkali halides were introduced. Highly mobile recombining centers (H centers) diffused to the colloid with a flux that was approximately equal to the flux of F centers. At the surface, the H center and 1 surface alkali-metal atom of the colloid, recombined. The lattice was also assumed to be subject to continuously generated radiation-induced excitations. At the surface of the colloid, the excitations resulted in displacements which distorted the surface of the growing cluster. It was concluded that the F centers did not condense into one compact cluster but were instead spread over a limited region which contained small sub-clusters. The spread increased considerably when the annihilation fraction was increased to above 80%. The surface displacements caused roughening of the cluster surface.

J.Seinen, P.J.Van Maaren, H.W.Den Hartog: Journal of Physics - Condensed Matter, 1994, 6[43], 9053-64