The kinetics of F-center aggregation under irradiation: many-particle effects in ionic solids

The accumulation kinetics of primary Frenkel defects created in solids under permanent irradiation is calculated using the microscopic formalism of many-particle densities. It is based on the Kirkwood superposition approximation for three-particle densities as described in our previous paper [V. N. Kuzovkov and E. A. Kotomin, Physica Scripta 47, 585 (1993)]. This formalism is generalized in this paper by incorporating the elastic attraction between similar defects (called in ionic solids F-centers) which causes their efficient aggregation. It is shown that the aggregation process starts only if the dose rate and elastic attraction energy exceed certain critical values; it also happens in the limited temperature interval, in agreement with experimental data known for NaCl crystals. Results obtained are compared with those of the mesoscopic approach. (orig.)