The Production of Molecular Positronium

The introduction of positron trapping techniques over the last decade or so has made possible a number of new experimental areas, and has revitalized the field of low energy positron physics. Positron plasmas stored in traps have been used to create beams of unprecedented quality for precision atomic physics experiments, and have also been invaluable in the production of low energy antihydrogen. Another area in which these methods have proved to be useful is in studies of systems containing more than one positron, which had not previously been feasible. By capturing tens of millions of particles in an accumulator and then releasing them in a short burst it is possible to create instantaneous positron currents in excess of 10 mA. Implanting such bursts into an appropriate target can lead to the formation of positronium atoms that are able to interact with one another. An obvious outcome of such interactions is the formation of molecular positronium, which we have observed on both the internal surfaces of porous silica and on the surface of an atomically clean Al(111) crystal. In this presentation I shall outline the techniques we have used to study interactions between positronium atoms, in particular the observation of molecular positronium, and discuss some of the experiments currently in progress.