Molecular-Dynamics Simulations of Ballistic Damages Caused by an Energetic Recoil Nucleus on a Nuclear Glassy Network

Abstract

ABSTRACTWe have studied the damage caused by an energetic recoil nucleus on the glassy network, from a ballistic viewpoint, using molecular dynamics method. The energies of the displacement cascades performed have been limited to 6keV up to now. This energy represents approximately one tenth of the energy of a recoil nucleus emitted during ca disintegrations in a real nuclear glass. The composition studied comprises the major elements of the real glass: SiO2, B203, Na20, A1203, ZrO2, and the atomic interactions are represented by Born-Mayer-Huggins potentials with formal atomic charges completed by three-body terms. The study described here must be considered in the light of earlier studies in which the authors investigated the complete sequence of a displacement cascade, revealing atom movements occurring when the Coulomb force field is modified in the glass matrix.As in the ballistic collision sequence, network formers and modifiers exhibit different behaviour. Network modifiers react more quickly and more violently to a modification of the Coulomb field, and relaxation of the alkali metal atoms occurs together with the relaxation of the three-dimensional network of formers. Relaxation of the alkali metals is a key factor ensuring more thorough relaxation of the network formers; the authors have previously shown that preventing relaxation of the alkali metals limits network relaxation.A more comprehensive description of a displacement cascade can thus be proposed. It is important to distinguish between the ballistic collision sequence per se, which begins first and displaces mainly network formers and oxygen atoms by individual movements, and the network relaxation sequence due to modification of the Coulomb fields, which begins with a slight delay following the collision sequence.