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 γ_{nl} for individual electron orbitals nl are found to scale with the ionization energy I_{nl} (in eV), as γ_{nl}=1+sqrt[A/I_{nl}]+(B/I_{nl})^{β}, where A≈40  eV, B≈24  eV, and β≈2.3.