Annealing of ion irradiation damage in nuclear graphite

Abstract

Changes in Raman spectra of polished and ion-irradiated Gilsocarbon and Highly Orientated Pyrolytic Graphite (HOPG) during annealing have been investigated and compared with changes reported during stored energy release in fast neutron irradiated graphite. It is postulated that the change in the Raman spectra of polished, ion-irradiated and neutron irradiated graphite can be attributed to crystalline structural changes due to the annealing of lattice defects. This is illustrated in this work by changes in the kinetic parameters, in terms of the decrease of the Raman ID/IG ratio, during the thermal annealing of polished and ion-irradiated Gilsocarbon and HOPG graphite. Several kinetic models are investigated in terms of activation energy and order of reaction. The most suitable model to explain Raman annealing kinetics was found to be, a two reaction model for polished Gilsocarbon graphite, and a two and possibly three reaction model for ion-irradiated Gilsocarbon graphite and ion-irradiated HOPG. The kinetics parameters obtained using both the two and three reaction models reveal similarities with kinetic models obtained for neutron irradiated graphite. The assumption that the Raman intensity ratio ID/IG is proportional to the square root of the defect quantity provided a better fit than the assumption of direct proportionality.