Modeling the processes of interaction of heavy ion beams and nanoclusters with condensed matter based on molecular-dynamic and quantum-field approaches using high-performance systems

This project is the last one of a series of one-year projects in the frame of the cooperation between Sofia University (SU) and the Joint Institute of Nuclear Research (JINR), Dubna, Russia.

JINR is an international intergovernmental organization, established on the basis of a Contract, signed back in 1956 by 11 founding countries, including Bulgaria. Since then the fruitful cooperation between JINR and Bulgarian Scientific institutions, including Sofia University has begun. Nowadays Bulgaria is one of the 18 JINR Member States.

Participants of the projects are scientist from the Faculty of Mathematics and Informatics (FMI), SU, Institute for Nuclear Research and Nuclear Energy, Bulgarian Academy of Sciences, Laboratory of Information Technologies (LIT), JINR.

Studies in the field of the irradiation of materials with high-energy heavy ions (HEHI) and nanoclusters have been carried out over recent decades. These studies include the following directions:

(i) determining the radiation resistance of construction materials;

(ii) studying of the processes of formation of tracks in the materials;

(iii) studying of the processes of evaporation (the emission of atoms from the surface of the irradiated materials).

(iv) studying of the ”long range effect” in metals, exposed to nanoclusters.

Studies in the above fields remain topical and in demand at present. Computer simulation requires development of new and improved existing models on the basis of new experimental data.

One of the main models of interaction of HEHI with metal samples is the thermal spike model, which is a system of equations of thermal conductivity for the electron gas and the crystal lattice. The thermal spike model is based on the idea of energy (heat) transfer from the electron gas to the lattice. This model has been used to study the interactions of HEHI with different materials for more than thirty years. Another model for studying the interaction of heavy ions with materials is the molecular dynamics method. It makes possible to obtain considerably more information on the studied system (temperature, pressure, change in the structure etc.). The thermal spike model is used for obtaining the initial conditions, which imitate the impact of HEHI on the molecular-dynamic system. Further evolution of the system is studied by the molecular dynamics method.

Continuous Atomistic Approach, implemented in the frame of the projects, combines these two models. To be efficient, this approach needs high performance computer systems and parallelization of the algorithms. The effectiveness of the worked out computational schemes and their parallel Open MP implementation are tested on the HybriLIT Heterogeneous Platform, JINR.

By using the techniques, mentioned above, the following processes are investigated:

(i) the processes of irradiation of nickel target by uranium ions of energy in the range of 100−700 MeV in the surface layer of the target;

(ii) the process of irradiation of a copper target with copper nanoclusters of energy 50 eV/atom;

The phenomenon called long range effect in metals irradiated by particles is investigated numerically. Important results are found for the structural changes in a copper target, irradiated simultaneously by several copper nanoclusters, when structural changes occur at a target depth, exceeding the penetration depth of the nanoclusters.

We hope, this fruitful cooperation will continue.