The behavior of the Ps atom in molecular substances, particularly liquids, is investigated. The pickoff rates of o-Ps in various liquid compounds are found to have a simple empirical relationship to the values of the surface tension of the liquids. The relationship is found to have a theoretical foundation. The Ps atom is highly localized in a cavity created by the balance of various molecular forces inside the liquid. From the above relationship, other simple relationships between the pickoff rates of o-Ps and the various properties of the medium, e.g., polarizability, cohesive energy density, etc., and the temperature or pressure changes can be derived and explained. The diffusion of o-Ps is discussed. A similar approach can also be used for molecular solids.

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Free volume dependent fluorescence property of PMMA composite: Positron annihilation studies AIP Conf. Proc. 1512, 126 (2013); 10.1063/1.4790943 Interlaboratory comparison of positron annihilation lifetime measurements for synthetic fused silica and polycarbonate J. Appl. Phys.The lifetimes of o-positronium in .silica gel adsorbed with various amounts of water, n-hexane, or nitro-ethan~ were measured. The fractIOn of o-positronium escaping the condensed phase can be related to t e specific area. ~nd the pore volume of the silica gel. The mean life of o-positronium in the pores is found t~ b~rvery sensItive to t~e surface properties of silica gel. The formation of free radicals on the surface o ISllca. and the reactIOns between these free radicals and o-positronium are suggested as the exp anatlOns.

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