Anisotropic magnetic quenching of positronium states in oriented crystals

We have carried out a theoretical analysis of the anisotropy of magnetic qu enching of positronium states in noncubic crystals oriented relative to the direction of the external magnetic field. We show that an initial polariza tion of the positrons amplifies the anisotropy of magnetic quenching of pos itronium and lowers the magnitude of the magnetic field in which the anisot ropy is maximum. We have obtained numerical estimates of the magnitude of t he experimentally observed effect for quasipositronium in a single crystal of crystalline quartz and for a positronium complex in a single crystal of naphthalene. (C) 1999 American Institute of Physics. [S1063-7834(99)01506-3 ].