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Topic: On the Role of Electronic Energy Loss on Radiation Damage in Materials

Speaker: Professor William J. Weber
　　 Department of Materials Science & Engineering, University of Tennessee, USA

Time: 10:00-11:30, (Mon.) Jun. 1^st, 2015

Venue: Room 403, Shi Changxu Building, IMR CAS

Abstract:

The interaction of ions with solids results in energy loss to both atomic nuclei and electrons. At low energies, nuclear energy loss dominates, and radiation damage occurs primarily by ballistic collisions between atomic nuclei. At high energies typical of fission products and swift heavy ions, electronic energy loss dominates, leading to intense local ionization and the formation of defects, latent tracks or recovery of pre-existing damage. At intermediate ion energies, nuclear and electronic energy losses are of similar magnitude and can lead to additive, competitive or even synergistic processes that affect damage production, defect recovery and microstructure evolution. This energy regime includes energies of primary knock-on atoms created by fission and fusion neutrons, energies of ions used to investigate neutron damage in materials, and ion energies used to modify or generate novel defects and structures in materials in order to tailor properties or create unique functionalities. We have integrated experimental and computational approaches to investigate the separate and combined effects of nuclear and electronic energy loss on the response of ceramics to ion irradiation over a range of energies. Experimentally, ion mass and energy are used to control the ratio of electronic to nuclear energy loss; whereas, large scale molecular dynamics simulations that include both ballistic collision processes and local heating, or inelastic thermal spike, from ionization via electron-phonon coupling are used to model these processes. Using these approaches, an additive effect of nuclear and electronic energy loss on damage production in amorphous silica and crystalline MgO is demonstrated over a wide range of energies. Similarly, the competitive effects of nuclear and electronic energy loss are confirmed for SiC, Ca₂La₈(SiO₄)₆O₂ and Fe. Finally, a synergistic effect of nuclear and electronic energy loss is observed in LiNbO3. These results have significant implications for modeling the response of materials to extreme radiation environments.