Speaker
Description
Research studies into the subject of radiation damage effects in graphite began in the early 1940’s as a part of the development of nuclear weapons and nuclear power research. Extensive measurements were performed to study changes to the thermal and mechanical properties of irradiated graphite. Many of these properties such as the thermal expansion coefficient, heat capacity, thermal conductivity, bulk modulus and elastic constants have some level of dependency on the vibrational spectrum. In this work, a series of measurements of the phonon densities of states of different samples of irradiated nuclear graphite were performed at room temperature using the state-of-art Wide Angular-Range Chopper Spectrometer (ARCS) at the neutron spallation source in Oak Ridge National Laboratory. The samples were exposed to different levels of neutron damage (up to $\approx30$ dpa) and irradiation temperatures (300--750$^\circ$C) [1]. The main differences in the phonon dispersion relations and phonon densities of states for samples with different irradiation conditions (damage and/or temperature) are identified. In addition, first-principles phonon density of states calculations of ideal and defected (di- and tetra-vacancy as well as single and di-interstitial) graphite are performed and compared with measured ones.
The irradiation of the specimens was performed at the Oak Ridge National Laboratory (ORNL) and sponsored by Tokai Carbon Co., Ltd. (NFE-09-02345) with the U.S. Department of Energy. A portion of this research at ORNL’s High Flux Isotope Reactor and the Spallation Neutron Source was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, US Department of Energy. Oak Ridge National Laboratory is managed by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 for the U.S. Department of Energy. Travel and time of I. I. Al-Qasir was supported by the University of Sharjah, UAE. This material is based upon work that was conducted by I. I. Al-Qasir while a Visiting Research Fellow at the Shull Wollan Center -- the University of Tennessee and Oak Ridge National Laboratory’s Joint Institute for Neutron Sciences. First-principles calculations were performed at the high-performance computing facility (SAQR) at the University of Sharjah.
Refs
[1] A. A. Campbell, Y. Katoh, M. A. Snead and K. Takizawa, {\it Property changes of G347A graphite due to neutron irradiation}, Carbon {\bf 109}, 860--873 (2016).
