Irradiation effect of Li2O with high energy oxygen ions

Lithium oxide is a prime candidate of tritium breeding blanket material for an experimental fusion reactor designed at Japan Atomic Energy Research Institute. During the operation of the fusion reactor, severe irradiation damage will be caused in Li2O by neutrons with energy up to 14 MeV, tritons of 2.7 MeV and helium ions of 2.1 MeV produced by Li-6 (n, α) H-3 reaction. Recently, the swelling of sintered Li2O pellets was observed in a fast neutron irradiation test using a FBR, EBR-2. In the formation of irradiation defects in Li2O, oxygen atoms are displaced as one kind of primary knock-on atoms (PKAs) by the fast neutrons, tritons and helium ions due to the reaction. Therefore, oxygen ion irradiation is essential to investigate the formation of defects. In this study, the formation process and the fundamental properties of the irradiation defects in Li2O, irradiated directly with oxygen ions as one kind of PKAs, were investigated by optical absorption and electron spin resonance (ESR) methods. The experiment and the results are reported. The electron excitation process seemed to play an important role in the formation of defects in Li2O. The recovery behavior of the defects was also examined. (Kako, I.)