Formation and quenching of ortho-positronium in molecular materials

A correlation is observed between the lifetime and two-photon annihilation intensity by pick-off process of ortho-positronium in molecular materials. An empirical model, in terms of free volume, is developed to explain this correlation. The variation in lifetime and intensity with change of temperature and pressure, and due to melting of crystals, and glass-transition in polymers is considered, on the basis of this model.