POSITRON NUCLEUS RESONANCES IN ELECTRIC AND MAGNETIC-FIELDS

Resonance states of a positron in the Coulomb field of a nucleus and i n parallel homogeneous electric and magnetic fields are studied. In th e classical description, the positron undergoes oscillatory motion alo ng the symmetry axis, being reflecting consecutively from the nucleus and the anode. The magnetic field does not permit the positron to go a round the nucleus and move to the cathode, stabilizing the resonances. The nucleus is regarded as infinitely heavy, and the problem reduces to a one-particle Schrodinger equation. The energies and widths of the resonances are determined by means of versions of perturbation theory in weak electric and strong magnetic fields, the 1/n expansion, and t he quasiclassical approximation. Different methods are in good agreeme nt with one another.