The time for positron thermalization in ionic crystals due to the interaction of positronic atoms with polarizational optical oscillations of the lattice is calculated. The positronic atom is considered as a dipole with moment p induced by the internal crystal field. The dipole moment is evaluated from the value of the positronic-atom deformation parameter determined from data on the magnetic quenching of positronium. For an NaCl crystal, p ≈ 1.91D. The positronium thermalization time in ionic, crystals (for the example of NaCl) is estimated at ∼10−1 sec. After this time, not only ortho positronium but also para positronium reached total thermalization.
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