Free-Positron Annihilation Mean Life in Diatomic and Rare Gases in Liquid and Solid States

Measurements have been made on the free-positron annihilation mean life, τ₁, in H₂, D₂, He, N₂, O₂, Ne, Ar, and Xe in liquid and/or solid states. To a fair approximation, the observed mean lives may be represented by the equation: τ₁(nsec)=0.31+0.15×10^-4Eᵢ²ρₑ, where Eᵢ is the first electron ionization potential in eV, and ρₑ is the number of outermost electrons per unit "atomic volmue" a₀³. In the H₂ and D₂ isotopes where Eᵢ is constant, τ₁ is linearly dependent on ρₑ^-1. It was also found that τ₁ is independent of the orthopara ratio of the liquid H₂ at 20.4^∘{}K.