Positronium in silica-based glasses

Structural subnanovoids in silica-based glasses (synthetic silica, borosilicate glass, lead glass, alkali barium glass, soda-lime glass and model glass of radioactive waste glass) with several SiO₂ concentrations are studied by positron lifetime and one-dimensional angular correlation of annihilation radiation spectroscopy. The average sizes of the structural subnanovoids are estimated from the pick-off annihilation rates of the ortho-positronium and from the momentum distribution of the para-positronium. It is observed that the sizes of the subnanovoids and the positronium intensities decrease with decreasing SiO₂ concentrations in the glasses, which suggests that the positronium is a unique and useful tool for subnanovoids in glass materials.