Annihilation of Positrons in Methane

Abstract
Positron lifetime spectra have been measured in methane gas at 23 °C over a density range of 5.0 × 104 to 1.5 × 102 g/cm3. Statistical analysis of the data yields a Zeff1 of 0.442 ± 0.019 for orthopositronium and a Zeff of 153.3 ± 0.6 for positrons which do not form positronium. Several annihilation mechanisms are discussed in connection with the data.