Laboratory Simulation of Direct Positron Annihilation in a Neutral-Hydrogen Galactic Environment

Abstract

The linewidth for thermalized positrons directly annihilating with bound electrons in low-density molecular hydrogen gas has been found to be 1.56 \ifmmode\pm\else\textpm\fi{} 0.09 keV, by use of a Ge detector with a low-energy pulsed positron beam. This linewidth measurement together with previous experimental results makes it possible to determine precisely the composite spectrum due to positrons annihilating in a neutral-hydrogen galactic medium.