POSITRONIUM LIFETIMES IS POROUS VYCOR GLASS

The ortho-positronium lifetimes in porous Vycor glass were measured in a wide range of pore radii. A good correlation of the most probable l ifetime with the model accounting for the population of upper levels o f a particle in the potential well was observed. For channel-like void s (capillaries in porous media) a new value of the empirical parameter , Delta R, entering in the semi-empirical Eldrup equation, is proposed : Delta R = (0.191 +/- 0.007) nm; it explains some of the discrepancie s previously found in crystalline solids. (C) 1998 Elsevier Science B. V. All rights reserved.