γ -Ray Spectra and Enhancement Factors for Positron Annihilation with Core Electrons

Many-body theory is developed to calculate the γ spectra for positron annihilation in noble-gas atoms. Inclusion of electron-positron correlation effects and core annihilation gives spectra in excellent agreement with experiment [K. Iwata et al., Phys. Rev. Lett. 79, 39 (1997)]. The calculated correlation enhancement factors γₙₗ for individual electron orbitals $nl$ are found to scale with the ionization energy Iₙₗ (in eV), as γₙₗ=1+√A/Iₙₗ+(B/Iₙₗ)^β, where A≈40 eV, B≈24 eV, and β≈2.3.