Annihilation of Positrons in Gases

Abstract

The angular correlation of the two-photon annihilation of positrons annihilating in gases at high pressures demonstrates the two modes of decay—(1) from a bound state, positronium, and (2) from an unbound state—in all gases tested that have low-lying energy states. The increase in the narrow component in argon, plus suitable thermalizing gases, due to the application of a dc magnetic field obeys the theoretical increase due to the mixing of the $1{}_{}{}^1{}_{}{}^{}S$ and $1{}_{}{}^3{}_{}{}^{}S$ $m=0\mathrm{}$ states. The increase in positronium formation due to the application of a dc electric field is observed. Preliminary evidence for the existence of $n=2\mathrm{}$ states of positronium is seen.