Dependence of orthopositronium annihilation rates on density fluctuations in methane gas

Abstract

Recent experiments have shown that the annihilation rate of positrons which form orthopositronium in methane gas varies linearly with gas density at low densities, but significantly deviates from linearity at high densities. We present evidence that this annihilation behavior in methane results from density fluctuations that are characteristic of an imperfect gas.