Study of radiation damage inLi2O by means of electron-spin resonance

ESR spectra with a hyperfine structure consisting of more than 20 peaks were observed in ${\mathrm{Li}}_2$O single crystals, irradiated by energetic tritons and helium ions formed by 6 × ${10}^{22}$ to 6×${10}^{25}$ ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$($n$, $\alpha$)-${}_{}{}^3{}_{}{}^{}\mathrm{H}$ reactions per ${\mathrm{m}}^3$ introduced with the order of ${10}^{20}$ to ${10}^{23}$ thermal neutrons per ${\mathrm{m}}^2$. The $g$ value of the spectra was 2.002±0.001, and the hyperfine structure depended on the orientation of the specimens relative to the applied magnetic field. From the angular dependence the spectra were attributed to $F^{+}$ centers (an oxygen vacancy trapping an electron). In ${\mathrm{Li}}_2$O single crystals irradiated to the order of ${10}^{23}$ thermal neutrons per ${\mathrm{m}}^2$, colloidal Li metal centers were not observed, in direct contrast with the situations in sintered ${\mathrm{Li}}_2$O pellets. Isochronal and isothermal annealing experiments were done and the recovery behavior of the $F^{+}$ centers was observed. From the isothermal annealing experiments, the activation energy for recovery of the $F^{+}$ centers was determined to be about 135 kJ/mol (1.4 eV).