Annihilation of positrons trapped at metal surface and possibility of occurrence of asymetry in angular distributions of annihilation quanta under the influence of an external electric field

A phenomenological, quantum-mechanical model of the annihilation of the positrons trapped at the metal surface in proposed. The model takes into account effects related to the interference of the electron waves incident and reflected from the metal-vacuum boundary. Conclusions drawn from the study of the scattering of the electron wave from the trapped positron indicate that the scattering process can cause an asymmetry in the distribution of the perpendicular (to the metal surface) component of the resultant momentum of the annihilation photon pair. Such asymmetry can also manifest itself in samples which contain voids, as a result of positron drift at the void surface under the influence of the applied electric field. An attempt is made to explain, in this way, the influence of the electric current flow in some metallic samples on the behaviour of the angular distributions of the annihilation photons. (author)