Nonlinear phenomena in the transfer of radiation in matter are caused by gradual changes of its composition and structure with the increase of irradiation dose. They represent one of the most urgent and complex problems of computational support of applied developments in the field of nuclear and irradiation technologies. In particular, it arises in applications, for this purpose, of statistical computer simulation of the impact of different types of irradiation (electron-photon, neutron, ion) on the properties of materials.

 Upgrade of the MD code MICKSER

We widely use the SPE RESST of NSC KIPT developed molecular dynamics (MD) code MICKSER in the fundamental and applied R&D of innovative materials and modification of their properties by means of ion implantation and solid surface treatment by ion beams.

The following upgrades of the MICKSER code were completed in year 2014:

 implementation of two methods of modeling of the accumulation of structural defects in irradiated crystalline material with the increase of an irradiation dose, the implicit method based on the well-known Kinchin-Pease model and the explicit one with detailed atomistic modeling of the atomic collision cascade;

 introduction of algorithms for simulation of ion transport in a radiation-damaged crystal subject to amorphization of the crystal target under irradiation and inter- and intracascade athermal annealing of point defects;

 a finite-difference calculation scheme was constructed to predict the evolution of the target structure and composition during implantation to high doses of ~1014?16 ions/cm2 in view of the their nonlinear inverse effect on the transport of ions and cascade atoms.

 The simulation results were compared with the experimental data on the profiles of boron and arsenic ions doped into the [001]Si crystallographic direction at implantation doses ranging from 10¹³ to 10¹⁵ cm^–2 (see Figure 1).

 It was shown that the profile shape changes with the growth of the dose due to the nonlinear effect and, in particular, the suppression of the long-range "tails" of the destructive channeling of ions occurs.

 The development opens the possibility of the MICKSER code efficient application for prediction of the materials irradiation after-effects at modification of their surface layers properties to depths of several hundred nanometers.

 For the same purpose, work has begun on the implementation into the code of the kinetic Monte Carlo method of simulation of the diffusion processes relevant to the evolution of defect structures in irradiated material, namely, the formation of complexes of radiation defects and the interaction of defects and impurities with sinks and, in particular, with elastic fields of dislocations.