Modeling of primary defect aggregation in tracks of swift heavy ions in alkali halides

Dynamic Monte Carlo simulations of primary defect aggregation in tracks of swift heavy ions in alkali halides have been performed. The study was motivated by recent experimental findings on dense F-center clusters observed even at 15 K in LiF irradiated by GeV heavy ions. We relied on a recently suggested model, which assumes local heating and diffusion of single defects in their excited electronic state. The main parameters (migration energy, initial defect concentration, diffusion time) are estimated from available experimental data. Simulation results confirm the formation of a core with large F-aggregates and a broad halo of single and dimer defects around it. The fraction of large (more than 10 defects) aggregates in the core is negligible, making ESR detection impossible. The low sensitivity of the model to changes in parameters can be explained by its universal features, which we first report in this paper. Unexpected power laws in the kinetics of single defect concentrations are also emphasized.