The positron lifetime measurements have been performed as a function of temperature for liquid methane and propane and as a function of magnetic field for liquid argon. The long o-Ps lifetime, high o-Ps intensity, and a strong temperature dependence of these values are observed, and interpreted as being due to the Ps localization in the bubble state. The bubble size and surface tension are evaluated using bubble model and o-Ps lifetime. The chemical reaction of Ps atom with oxygen impurities

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... studied. The reaction rate K, and its temperature behavior in liquid methane and propane were obtained. The results of magnetic field experiments in both pure and oxygen-added liquid argon show that the lifetime of o-Ps with magnetic quantum number m=O state decreases basically according to the normal Zeeman effect.