Positronium Spin Conversion by Phosphorescent Impurities in Gases

Abstract
Ultraviolet illumination of Ar, N2, or air containing trace amounts of SO2 or benzaldehyde quenches positronium through interactions with photoexcited impurity triplet states. The measured interaction cross sections are large, 104πa02, and appear to increase as T12 in the range 300 to 400°K. Triplet concentrations as low as 108 can be detected at atmospheric pressures.