DOUBLE IONIZATION WITH POSITRONIUM FORMATION IN POSITRON - ATOM COLLISIONS H. Bluhme, H. Knudsen#, J.P. Merrison and K. A. Nielsen Institute of Physics and Astronomy, Aarhus University, DK-8000 Aarhus C, Denmark In a recent series of measurements, we have shown that, surprisingly, for positron impact on He and Ne the channel which leads to double ionization of the target atom together with the formation of positronium is strongly suppressed. In this poster, we compare these results with similar experimental results obtained on Ar, Kr and Xe, as well as with the analogue process of fragmentation of molecules accompanied by positronium formation.