$γ$-ray spectra and enhancement factors for positron annihilation spectra with core-electrons

Abstract

Many-body theory is developed to calculate the $γ$-spectra for positron annihilation with valence and core electrons in the noble gas atoms. A proper inclusion of correlation effects and core annihilation provides for an accurate description of the measured spectra [Iwata \textit{et al.}, Phys. Rev. Lett. {\bf 79}, 39 (1997)]. The theory enables us to calculate the enhancement factors $γ_{nl}$, which describe the effect of electron-positron correlations for annihilation on individual electron orbitals $nl$. We find that the enhancement factors scale with the orbital ionization energy $I_{nl}$ (in electron-volt), as $γ_{nl}=1+\sqrt{A/I_{nl}}+(B/I_{nl})^β$, where $A\approx 40$~eV, $B\approx 24$~eV and $β\approx 2.3$.