Radiation Effects on Transport and Bubble Formation in Silicate Glasses

Using advanced magnetic resonance spectroscopies and small-cluster modeling, atomic structure of radiation-induced point defects in alkali borate, silicate, and borosilicate glasses is fully characterized. It is shown that in boron-containing glasses, most of these point defects are electrons/holes trapped by cation/anion vacancies, such as O1 - - O3 + valence-alternation pairs. In microscopically phase-separated borosilicate glasses, radiation-induced defects are found to cluster at the interface between the borate and silicate phases. Reaction and diffusion dynamics of defect-annealing interstitial hydrogen atoms in boron and silica oxide glasses are studied. The yield of radiolytic O2 is estimated. This oxygen is shown to be the final product of triplet exciton decay. Plausible mechanisms for the oxygen bubble formation are put forward. Two practical conclusions relevant for the EMSP mission are made: First, the yield of radiolytic oxygen is shown to be too low to interfere with the storage of vitrified radioactive waste in the first 10 Kyr. Second, microscopic phase separation is demonstrated to increase both the chemical and radiation stability of borosilicate glass