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, ${\tau }_1$, in ${\mathrm{H}}_2$, ${\mathrm{D}}_2$, He, ${\mathrm{N}}_2$, ${\mathrm{O}}_2$, Ne, Ar, and Xe in liquid and/or solid states. To a fair approximation, the observed mean lives may be represented by the equation: ${\tau }_1\left(\mathrm{nsec}\right)=0.31+0.15\mathrm{}\times {10}^{-4\mathrm{}}\frac{{E_i}^2}{{\rho }_e}$, where $E_i$ is the first electron ionization potential in eV, and ${\rho }_e$ is the number of outermost electrons per unit "atomic volmue" ${a_0}^3$. In the ${\mathrm{H}}_2$ and ${\mathrm{D}}_2$ isotopes where $E_i$ is constant, ${\tau }_1$ is linearly dependent on ${{\rho }_e}^{-1\mathrm{}}$. It was also found that ${\tau }_1$ is independent of the orthopara ratio of the liquid ${\mathrm{H}}_2$ at 20.4°K.