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 $1^{3}S$ $m=0$ states. The increase in positronium formation due to the application of a dc electric field is observed. Preliminary evidence for the existence of $n=2$ states of positronium is seen.