Enhancement Factors for Positron
Annihilation on Valence and Core
Orbitals of Noble-Gas Atoms
D. G. Green and G. F. Gribakin
Abstract Annihilation momentum densities and vertex enhancement factors for
positron annihilation on valence and core electrons of noble-gas atoms are calculated using many-body theory for s, p and d-wave positrons of momenta up to the
positronium-formation threshold. 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 almost 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.
Keywords Positron annihilation ⋅ Annihilation momentum density
Many-body theory ⋅ Enhancement factors ⋅ Noble-gas atoms
1 Introduction
Low-energy positrons annihilate in atoms and molecules forming two í µí»¾ rays whose
Doppler-broadened spectrum is characteristic of the electron velocity distribution in
the states involved, and thus of the electron environment. This makes positrons a
unique probe in materials science. For example, vacancies and defects in semiconductors and other industrially important materials can be studied [1–6]. Positroninduced Auger-electron spectroscopy (PAES) [7–11] and time-resolved PAES
[11, 12] enable studies of surfaces with extremely high sensitivity, including dynamics of catalysis, corrosion, and surface alloying [13]. The í µí»¾ spectra are also sensitive
to the positron momentum at the instant of annihilation. This is exploited in AgeD. G. Green ( ✉ ) ⋅ G. F. Gribakin
Centre for Theoretical Atomic, Molecular and Optical Physics,
Queen’s University Belfast, Belfast, Northern Ireland BT71NN, UK
e-mail: d.green@qub.ac.uk
G. F. Gribakin
e-mail: g.gribakin@qub.ac.uk
© Springer International Publishing AG, part of Springer Nature 2018
Y. A. Wang et al. (eds.), Concepts, Methods and Applications of Quantum Systems
in Chemistry and Physics, Progress in Theoretical Chemistry and Physics 31,
https://doi.org/10.1007/978-3-319-74582-4_14
243
Annihilation on Valence and Core
Orbitals of Noble-Gas Atoms
D. G. Green and G. F. Gribakin
Abstract Annihilation momentum densities and vertex enhancement factors for
positron annihilation on valence and core electrons of noble-gas atoms are calculated using many-body theory for s, p and d-wave positrons of momenta up to the
positronium-formation threshold. 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 almost 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.
Keywords Positron annihilation ⋅ Annihilation momentum density
Many-body theory ⋅ Enhancement factors ⋅ Noble-gas atoms
1 Introduction
Low-energy positrons annihilate in atoms and molecules forming two í µí»¾ rays whose
Doppler-broadened spectrum is characteristic of the electron velocity distribution in
the states involved, and thus of the electron environment. This makes positrons a
unique probe in materials science. For example, vacancies and defects in semiconductors and other industrially important materials can be studied [1–6]. Positroninduced Auger-electron spectroscopy (PAES) [7–11] and time-resolved PAES
[11, 12] enable studies of surfaces with extremely high sensitivity, including dynamics of catalysis, corrosion, and surface alloying [13]. The í µí»¾ spectra are also sensitive
to the positron momentum at the instant of annihilation. This is exploited in AgeD. G. Green ( ✉ ) ⋅ G. F. Gribakin
Centre for Theoretical Atomic, Molecular and Optical Physics,
Queen’s University Belfast, Belfast, Northern Ireland BT71NN, UK
e-mail: d.green@qub.ac.uk
G. F. Gribakin
e-mail: g.gribakin@qub.ac.uk
© Springer International Publishing AG, part of Springer Nature 2018
Y. A. Wang et al. (eds.), Concepts, Methods and Applications of Quantum Systems
in Chemistry and Physics, Progress in Theoretical Chemistry and Physics 31,
https://doi.org/10.1007/978-3-319-74582-4_14
243