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  • 1 Maria Curie-Skłodowska University Institute of Physics 20-031 Lublin (Poland)
  • 2 Maria Curie-Skłodowska University Department of Crystallography, Faculty of Chemistry 20-031 Lublin (Poland)
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Experimental values of o-Ps lifetime were compared with model calculations, approximating the voids in a solid by spheres or cuboids. In the case of resorcinol the model of spherical voids is well consistent with the experimental data. For channel-like free volumes the formula, analogous to that for spheres, gives systematically the values of o-Ps lifetime too large. No positronium is found in anthracene, although the radius of free volume is larger than 0.97 Å at which the Ps binding energy should be zero.