POSITRON-ANNIHILATION IN GASEOUS-HYDROGEN AND HYDROGEN-NEON MIXTURES .1. LOW-ENERGY POSITRONS

Annihilation lifetime spectra have been measured for positrons in H2 gas at 293, 250, and 77 K at densities in the range 5.9-429 amagat, and in H2-Ne gas mixtures at 77 K having H2 partial densities in the range 1.9-286 amagat and with Ne concentrations in the range 0.02-0.98. The annihilation rate of slow positrons with H2 has a complex dependence on gas density and temperature. Particularly at low H2 densities, the presence of various partial densities of Ne can dramatically affect the positron-H2 annihilation process. The slow-positron annihilation rates are discussed in terms of positron-H2 collision complexes and the self-trapping of positrons within clusters of H2 molecules. The annihilation in H2 of positrons bound in Ps atoms is discussed in paper II of this series. © 1979 The American Physical Society.