RETENTION ANS DESORPTION BEHAVIORS OF HYDROGEN ISOTOPES IN GAMMA-RAY IRRADIATED Li_2TiO_3

摘要

Annihilation behaviors of irradiation defect and, correlation of these behaviors with deuterium trapping and desorption in gamma-ray irradiated Li_2TiO_3, which is one of the candidates for tritium breeding material, were studied by means of an ESR(Electron Spin Resonance) method and TDS (Thermal Desorption Spectroscopy). From the ESR spectra, gamma-ray irradiation induced irradiation defects such as E'-centers, oxygen-hole centers which were expected to be tritium trapping sites. These irradiation defects were annihilated in the temperature range of 500-650 K. From the TDS spectra for Li_2TiO_3 exposed to D_2 gas, the deuterium desorption behavior was found to consist of four stages, corresponding retention as the surface, in E'-center and as hydroxides bound with Ti or Li. In addition, most of deuterium was released as water form around 400, 550 and 650K. By comparison of the amounts of the deuterium retentions with or without the gamma-ray irradiation, the retention of deuterium trapped with the irradiation defects was increased by gamma-ray irradiation, indicating that the irradiation defects like E'-centers induced by gamma-ray irradiation would be one of the tritium trapping sites in tritium breeding materials. The activation energy of hydrogen isotope desorption from the E'-center was estimated to be 0.63 eV for gamma-ray irradiated Li_2TiO_3, showing good agreement with that of the recombination reaction between the E '-center and the oxygen-hole center. These results indicated that the tritium desorption was governed by the annihilation of the E'-centers.