Gaseous reactions involving positronium

Abstract

The problems involved in providing a detailed interpretation of the processes involved in the ultimate fate of positrons slowed down in a gas are examined by considering the idealized case of a gas of atomic hydrogen. The processes leading to the formation and dissociation of positronium are considered as well as those which lead to the slowing down of a positronium pair in a gas and to the conversion of ortho- into para-positronium. It is shown that the rate of the latter process probably depends strongly on the kinetic energy of the pair. Elastic collisions of a pair, in its ground state, with gas atoms are determined almost completely by electron exchange interaction, but this is so strong that it cannot be taken account of in a weak coupling treatment.