Enhancement factors for positron annihilation on valence and core orbitals of noble-gas atoms

Annihilation momentum densities and correlation enhancement factors for low-energy positron annihilation on valence and core electrons of noble-gas atoms are calculated using many-body theory. s, p and d-wave positrons of momenta up to the positronium-formation threshold of the atom are considered. The enhancement factors parametrize the effects of short-range electron-positron correlations which increase the annihilation probability beyond the independent-particle approximation. For all positron partial waves and electron subshells, the enhancement factors are found to be relatively insensitive to the positron momentum. The enhancement factors for the core electron orbitals are also independent of the positron angular momentum. The largest enhancement factor (∼ 10) is found for the 5p orbital in Xe, while the values for the core orbitals are typically ∼ 1.5.