Positron scattering and annihilation in neon gas

The lifetimes of positrons have been measured in pure neon gas with and without the application of an electric field and in neon-nitrogen mixtures. The results for pure neon are complicated by not quite pure exponential decays and internal consistency arguments have been used to set minimum values upon the equilibrium (or thermal) value of Zsub(eff) and upon the thermalization time. Annihilation in neon-nitrogen mixtures provides an extrapolated Zsub(eff) for thermal positrons of 6.02+-0.16. This result is consistent with the results for pure neon and enables the thermalization time to be set at a minimum value of 2700 ns amagat. Comparison with the theory of Montgomery and LaBahn and also with the phase shifts of Jaduszliwer and Paul suggests that the true thermalizaton time in pure neon may be more than twice this value, the possible discrepancy being explainable on the basis of one to two parts per million polyatomic impurity in the neon gas. The Zsub(eff) of Montgomery and LaBahn in the '2p→d and 2s→p norm.' approximation is 20% higher than the experimental value. Results under electric field show no unexpected features up to 31.9 V cm-1 amagat-1. (author)