FORMATION OF POSITRONIUM JETS BY IMPACT OF ULTRARELATIVISTIC POSITRONS ON ATOMS D. N. Aguilera, O. A. Fojon and R. D. Rivarola Instituto de Fisica Rosario (CONICET-UNR), Av. Pellegrini 250, 2000 - Rosario, Argentina Positronium formation is studied for impact of ultra-relativistic positrons on atomic targets. Matrix distorted wave models previously developed for heavy projectiles are employed. Matrix distortions are used to describe the electron simultaneously in the fields of the projectile and target nucleus. Differential and total cross sections for different targets at several positron velocities are presented.