“…2 The lifetime of localized orthopositronium (o-Ps; Ps is an e ϩ -e Ϫ bound state͒ has been experimentally and theoretically established as a measure of void size for pore diameters Ͻ1 nm, 3,4 and for deriving poresize distributions. 2 The lifetime of localized orthopositronium (o-Ps; Ps is an e ϩ -e Ϫ bound state͒ has been experimentally and theoretically established as a measure of void size for pore diameters Ͻ1 nm, 3,4 and for deriving poresize distributions.…”