Dynamic Effect of Neutron Irradiation in Damaging process of Ceramics and Glasses

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Dynamical measurements of the ion induced luminescence and in-reactor luminescence of SiO_2 glass have been performed. First the dynamic effect of the ion induced luminescence is compared between D^+ and He^+ ion irradiations, then the time evolution of the in-reactor luminescence change with neutron fluence are compared with those observed in the ion induced luminescence. Finally the origin of the luminescence center is discussedThe luminescence spectra of silica glasses induced by D^+ and He^+ irradiation have been found to be very similar to cathodoluminescence originated from the centers associated with oxygen vacancies and the intensity is proportional to the deposited energy by electron excitation irrespective of incident ion species. The luminescence intensity changes with the ion fluence, first increased, taking maximum and then gradually decreases to the nearly steady value after prolonged irradiation. When the fluence is converted to dpa (displacement per atom) value, changes of the luminescence intensity under D^+ and He^+ irradiations are very similar. From dynamical change of the luminescence intensify, the first increase of the luminescence intensity is attributed to the increase of newly produced point defect or oxygen deficiency due to the atomic displacement, while the decrease to the association of the point defects, for example, formation of Si segregation or more complex defects. In-reactor luminescence also reveals intensity increase caused by displacement effect of neutron.The present work clearly demonstrates that the dynamic measurement of the neutron and ion induced luminescence will give detailed information on the process of the defect formation in optically transparent materials