9:30 AM - **V1.1
Effects of Ionization on Irradiation Damage Evolution and Thermal Recovery in Ceramics.
William Weber 1 , Yanwen Zhang 2 , Ram Devanathan 1 Show Abstract
1 Fundamental & Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, Washington, United States, 2 Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, Washington, United States
Irradiation with energetic electrons and ions results in the transfer of energy to both atomic nuclei and the electronic structure. Kinetic energy transfer to atomic nuclei results in energetic atomic displacements and the production of atomic-level defects, while ionization energy loss to the electronic structure generates electron-hole pairs and localized electronic excitations. The understanding and modeling of atomic collision cascades and their role in irradiation damage evolution is well advanced. The effects of ionization are less understood. In ceramics, the localized electronic excitations can result in localized charge at defects and interfaces, rupture or change in nature of covalent and ionic bonds, enhanced defect and atomic diffusion, and changes in phase transformation dynamics, which affect the dynamics of atomic processes and the interpretation of the results from ion and electron irradiation experiments. Under irradiation with different ions, the ratio of electronic to nuclear stopping powers varies locally for both the primary ion and the secondary recoils produced. It will be shown that the critical temperature for ion-beam induced amorphization can exhibit a strong dependence on the ratio of electronic to nuclear stopping, which demonstrates that the local rate of in-cascade ionization has a significant effect on the dynamic recovery processes that determine the critical temperatures. Simultaneous electron and ion irradiation are shown to dramatically affect the dynamics of damage accumulation. In post-irradiation studies of ion-irradiated materials, ionization-enhanced recovery and recrystallization due to electron beam irradiation are observed, and the kinetics of the enhanced recovery processes has been determined. In the case of high-energy heavy ions (~0.1 to 2 GeV), such as fission fragments or swift-heavy ions, the intense energy deposition into the electronic structure produces a thermal spike. Computer simulations of thermal spikes in a range of materials demonstrate that the damage produced can range from the production of isolated point defects and defect clusters to the formation of tracks with fine structure.
10:00 AM - V1.2
The Need for Quantum Mechanics in Large-scale Atomistic Simulations of Radiation Damage in Metals.
C. Race 1 , D. Mason 1 , M. Finnis 1 2 , W. Foulkes 1 , A. Horsfield 2 , T. Todorov 3 , A. Sutton 1 Show Abstract
1 Department of Physics, Imperial College London, London United Kingdom, 2 Department of Materials, Imperial College London, London United Kingdom, 3 School of Mathematics and Physics, Queen’s University Belfast, Belfast United Kingdom
It has long been recognised that electronic excitations caused by high velocity particles in metals are central to understanding how these particles are slowed down. Quantum mechanics has played a key role in modelling such processes in idealized free electron gases (jellium models). The imperative now is to develop quantum mechanical treatments of metals with real atomic structures for large-scale atomistic simulation of radiation damage. In this paper we present an example of such large-scale simulation applied to the phenomenon of channelling.When a particle with a high kinetic energy enters a crystalline solid it may travel large distances along channels in the crystal structure. This process is called channelling. It plays a central role in determining the depth of irradiation damage suffered by materials exposed to high energy incident particles in nuclear reactors and in ion implantation. A key question centres on the mechanisms by which such a high energy particle loses its energy as it rattles down a channel in the crystal. It is known that at very high energies the principal mechanism is electronic, that is the channelling particle creates electronic excitations and gradually loses its energy until it has slowed sufficiently to create a cascade of atomic displacements. We present a simulation of this process based on solving t