Interaction between slow positrons and atoms

Relativistic many-body perturbation theory and a qualitative estimation of non-perturbative effects are used to calculate low energy scattering and annihilation of a positron with noble gas atoms. The existence of a virtual level (resonance) and an annihilation enhancement factor that is produced by the strong e + e − correlation, is demonstrated for heavy atoms (e.g. Xe and Rn). For molecules, (e + Xe n , e + Rn n , n ⩾ 2) the virtual level can transform into a real bound level for the positron. These results can explain the very high annihilation rate and non-linear dependence on atomic density observed in measurements of positron decay rates in dense xenon gas. The absence of such effects in a e + -Ne system completes the picture.