State Conversion of Positronium by Oxygen

Abstract：

Using a silica aerogel sample filled with oxygen gas as a variable energy positronium source, the effect of the positronium motion in oxygen has been investigated with a time selecting energy spectrometer. The positronium state conversion in an inelastic collision between the fast positronium atom and oxygen molecule has been verified and the conversion cross sections are measured as 2.1×10^-17 cm² and 6.6×10^-18 cm² respectively at the kinetic energies of positronium near two thresholds. For the slow positronium, the conversion cross section due to the exchange of electrons in the elastic collision is found to be proportional to 1/√v, where v is the mean velocity of positronium. This process would provide a clean para-positronium source for other precise experiments.