Anomalies of positronium atom annihilation in crystals

Full text: Positronium atoms (Ps) of both large and small radii in crystals contribute markedly to annihilation process of positrons. Early an anomalies positron annihilation in ionic crystals were explained using in exciton model of Ps of a large radius with a potential of interaction between an electron of an effective mass m-* and positron of an effective mass m+* written in the following form u=-e2/εr (ε is the optical permittivity, r is distance, and e is the charge). The calculated Ps characteristics were fitted to experimental data only assuming that ε→1, so that the effect off reduced mass Ps on its properties in a crystal inherent in model of a small radius Ps turned out prevailing. For this reason in this communication, the properties of Ps of a small radius were studied within the Winner-Frenkel model. Calculations within the Winner-Frenkel exciton model have shown that the basic crystal characteristics governing the Ps properties are the effective mass m-* and positron the effective mass m+* distinct from the masses of the free particles. Whenever m+*>>m-*, Ps exhibits extraordinary strong anomalies of its annihilation characteristics in crystal