Current Problems and Unknowns in Positronium Dynamics

A survey is made on positronium dynamics in liquids. From literature data, it is shown that applying conventional kinetics to positronium reactions leads to quite satisfactory results in a large variety of solvents, solutes, reaction types and temperatures. On the opposite, applying the theoretically well established concepts of positronium bubble state and time-dependent reaction rate coefficient would imply the use of unrealistic solute radii in the related kinetic equations, with possible exception of large solutes (micelles). Some solutes displaying unexpectedly high reaction rate constants are shown to be refractory to any of the above quantitative approaches. The particular case of reversible positronium bound-state formation is further examined, the most consistent results arising, again, from the conventional analysis of the data.