Dynamics of Radiation Damage in a Body-Centered Cubic Lattice. II. Higher Energies

Abstract

Computer studies in the dynamics of radiation damage in a body-centered cubic lattice representing $\ensuremath{\alpha}$ iron are extended to knock-on energies up to 1500 eV. The mean number ${N}_{d}$ of defects created is calculated first for a knock-on of 100 eV in a large variety of directions. In one representative direction the knock-on energy is varied up to 1500 eV. It is seen that ${N}_{d}$ increases approximately linearly with knock-on energy $E$. The usual formula ${N}_{d}=\frac{E}{2{E}_{d}}$ can be used with an effective threshold energy ${E}_{d}$ of 50 to 55 eV. Dynamic features of a single collision and a cascade of collisions are investigated. The free-atom binary model is not adequate for a single collision for the purpose of estimating the transfer of kinetic energy. In a cascade, the initially localized kinetic energy of the knock-on is seen, in a relatively short time, to divide into equal amounts of potential energy in the lattice and total kinetic energy of moving atoms. The process of channeling of an iron atom projected into the lattice along a low-index direction is studied with the same model. The range of the channeled atom is found to be proportional to the $\frac{3}{2}$ power of its initial energy, in disagreement with the predictions of the impulse approximation and in agreement with recent experiments.