Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Physical Review A

Pick-off annihilation in positronium scattering from alkali-metal ions

Igor A. Ivanov, Jim Mitroy

Published Mar 1, 2002• 9 citations
Publisher

Abstract

When orthopositronium collides with a closed-shell atom or ion the ``pick-off'' process is the dominant process for positron annihilation. In pick-off annihilation the positron annihilates with electrons in the target but not with the electron that is part of the positronium atom. The rate for pick-off annihilation, expressed in terms of the dimensionless parameter ${}^{1}{Z}_{\mathrm{eff}},$ for orthopositronium scattering from ${\mathrm{Li}}^{+},{\mathrm{Na}}^{+},$ and ${\mathrm{K}}^{+}$ was computed with an ${L}^{2}$ variant of the fixed-core stochastic variational method. The threshold ${}^{1}{Z}_{\mathrm{eff}}$ for ${\mathrm{Li}}^{+}$ and ${\mathrm{Na}}^{+},$ which can form a stable bound state with Ps were found to be 0.067 and 0.73, respectively, while that for ${\mathrm{K}}^{+},$ which does not bind Ps, was 0.064.

DOI
10.1103/physreva.65.034709

Related papers

Positronium scattering from closed-shell atoms and ions

Jim Mitroy, Igor A. Ivanov

The scattering of orthopositronium from He, Ne, Ar, ${\mathrm{Li}}^{+},$ ${\mathrm{Na}}^{+},$ and ${\mathrm{K}}^{+}$ is investigated with the fixed-core stochastic variational method. The scattering length for $\mathrm{Ps}\ensuremath{-}\mathrm{He}$ scattering was ${1.57a}_{0},$ a value consistent with the threshold cross sections derived from three positron lifetime experiments. The scattering lengths for the $\mathrm{P}\mathrm{s}\ensuremath{-}\mathrm{N}\mathrm{e}$ and $\mathrm{P}\mathrm{s}\ensuremath{-}\mathrm{A}\mathrm{r}$ systems were ${1.55a}_{0}$ and ${1.79a}_{0},$ respectively. That there was only a 15% variation among the scattering lengths is compatible with the experiment of Coleman et al. [J. Phys. B 27, 981 (1994)], who found the low-energy cross sections for He, Ne, and Ar to be about the same size. The scattering lengths for Ps scattering from ${\mathrm{Li}}^{+},$ ${\mathrm{Na}}^{+},$ and ${\mathrm{K}}^{+}$ were ${12.9a}_{0},$ ${28.5a}_{0},$ and $\ensuremath{-}{1.9a}_{0}.$ The relatively small magnitude of the ${\mathrm{P}\mathrm{s}\ensuremath{-}\mathrm{K}}^{+}$ scattering length strongly supports previous suggestions that the ${\mathrm{P}\mathrm{s}\ensuremath{-}\mathrm{K}}^{+}$ system does not support a bound state. The annihilation parameter ${}^{1}{Z}_{\mathrm{eff}}$ has also been computed as part of the analysis. The present values of ${}^{1}{Z}_{\mathrm{eff}}$ are about 2.5--3 times smaller than the accepted experimental values since short-range electron-positron correlations were not taken into consideration when the annihilation matrix element was evaluated.

Physical Review A•Dec 14, 2001•44 citations

Positronium scattering from Kr and Xe at low energies

Jim Mitroy, M. W. J. Bromley

The scattering of orthopositronium from Kr and Xe is investigated with the fixed core stochastic variational method. The scattering lengths for Ps-Kr and Ps-Xe scattering in the fixed core approximation are ${3.18a}_{0}$ and ${3.82a}_{0},$ respectively. Inclusion of core-polarization potentials leads to a significant reduction in the scattering lengths. The Ps-Kr and Ps-Xe scattering lengths were ${1.98a}_{0}$ and ${2.29a}_{0}$ for polarization potentials that were tuned to an average of the model electron-atom and positron-atom scattering lengths for the respective atoms. Other choices of the polarization potential resulted in scattering lengths that could be larger by ${0.3a}_{0}$ or smaller by ${0.8a}_{0}.$ The pick-off annihilation parameter ${}_{1}{Z}_{\mathrm{eff}}$ has also been computed as part of the analysis. The present values of ${}_{1}{Z}_{\mathrm{eff}}$ are about 3 to 10 times smaller than the accepted experimental values since short-range electron-positron correlations were ignored when the annihilation matrix element was evaluated.

Physical Review A•Mar 17, 2003•24 citations

Determination and applications of enhancement factors for positron and ortho-positronium annihilations

Jim Mitroy

Electron-positron annihilation rates calculated directly from the electron and positron densities are known to underestimate the true annihilation rate. A correction factor, known as the enhancement factor, allows for the local increase of the electron density around the positron caused by the attractive electron-positron interaction. Enhancement factors are given for positrons annihilating with the $1s$ electron in H, ${\mathrm{He}}^{+}$, He, ${\mathrm{Li}}^{2+}$, and ${\mathrm{Li}}^{+}$. The enhancement factor for a free positron annihilating with ${\mathrm{He}}^{+}$ and He is found to be close to that of ortho-positronium (i.e., Ps in its triplet state) annihilating with these atoms. The enhancement factor for Ps-He scattering is used in conjunction with the known annihilation rate for pickoff annihilation to derive a scattering length of $1.47{a}_{0}$ for Ps-He scattering. Further, enhancement factors for ${e}^{+}$-Ne and ${e}^{+}$-Ar annihilation are used in conjunction with the pickoff annihilation rate to estimate scattering lengths of $1.46{a}_{0}$ for Ps-Ne scattering and $1.75{a}_{0}$ for Ps-Ar scattering.

Physical Review A•Dec 16, 2005•12 citations

Spin-Orbit Quenching of Positronium during Atomic Collisions

Jim Mitroy, S. A. Novikov

When positrons are injected into a gas, 75% of the positronium (Ps) is likely to be formed as long-lived ortho-Ps. The main decay mechanisms for the ortho-Ps have been assumed to be natural decay of ortho-Ps and pickoff annihilation of the positron during Ps-atom collisions. A third possibility for annihilation is $\mathrm{o}\mathrm{r}\mathrm{t}\mathrm{h}\mathrm{o}\mathrm{\text{\ensuremath{-}}}\mathrm{P}\mathrm{s}\ensuremath{\rightarrow}\mathrm{p}\mathrm{a}\mathrm{r}\mathrm{a}\mathrm{\text{\ensuremath{-}}}\mathrm{P}\mathrm{s}$ conversion due to the spin-orbit interaction between the atom and colliding Ps. This extra quenching mechanism may explain a number of phenomena observed in the annihilation spectrum of Kr and Xe, including the very small Ps fraction of 3% seen for Xe.

Physical Review Letters•May 8, 2003•29 citations

Positronium-ion spin states in the scattering of polarized orthopositronium

Sudha Swaminathan

Abstract A single rearrangement collision between two spin-polarized orthopositronium beams leading to the production of either negative or positive positronium ions is studied. Negative or positive ions can be produced by the attachment of an electron or positron to a positronium atom, respectively. The probabilities for the formation of all possible spin states for both types of positronium ions are determined. The spin scattering matrix constructed using angular-momentum coupling as well as the spin density matrix containing the probabilities are given. The probabilities depend on the angle between the polarization vectors of the incoming beams and the real parts of complex scattering amplitudes labeled with total electron and total positron spin. We describe the effect of the spin alignment between the two beams on the probabilities and how the annihilation rates for ion decay and the real parts of the amplitudes can be obtained.

Journal of Physics B Atomic Molecular and Optical Physics•Sep 9, 2026•0 citations

Detecting Positron-Atom Bound States through Resonant Annihilation

V. A. Dzuba, V. V. Flambaum, G. F. Gribakin

A method is proposed for detecting positron-atom bound states by observing enhanced positron annihilation due to electronic Feshbach resonances at electron-volt energies. The method is applicable to a range of open-shell transition-metal atoms which are likely to bind the positron: Fe, Co, Ni, Tc, Ru, Rh, Sn, Sb, Ta, W, Os, Ir, and Pt. Estimates of their binding energies are provided.

arXiv:1007.4033•Physical Review Letters•Nov 9, 2010•37 citations
When orthopositronium collides with a closed-shell atom or ion the ``pick-off'' process is the dominant process for positron annihilation. In pick-off annihilation the positron annihilates with electrons in the target but not with the electron that is part of the positronium atom. The rate for pick-off annihilation, expressed in terms of the dimensionless parameter 1Zeff,{}^{1}{Z}_{\mathrm{eff}},1Zeff​, for orthopositronium scattering from Li+,Na+,{\mathrm{Li}}^{+},{\mathrm{Na}}^{+},Li+,Na+, and K+{\mathrm{K}}^{+}K+ was computed with an L2{L}^{2}L2 variant of the fixed-core stochastic variational method. The threshold 1Zeff{}^{1}{Z}_{\mathrm{eff}}1Zeff​ for Li+{\mathrm{Li}}^{+}Li+ and Na+,{\mathrm{Na}}^{+},Na+, which can form a stable bound state with Ps were found to be 0.067 and 0.73, respectively, while that for K+,{\mathrm{K}}^{+},K+, which does not bind Ps, was 0.064.
The scattering of orthopositronium from He, Ne, Ar, Li+,{\mathrm{Li}}^{+},Li+, Na+,{\mathrm{Na}}^{+},Na+, and K+{\mathrm{K}}^{+}K+ is investigated with the fixed-core stochastic variational method. The scattering length for $\mathrm{Ps}\ensuremath{-}\mathrm{He}$ scattering was 1.57a0,{1.57a}_{0},1.57a0​, a value consistent with the threshold cross sections derived from three positron lifetime experiments. The scattering lengths for the $\mathrm{P}\mathrm{s}\ensuremath{-}\mathrm{N}\mathrm{e}$ and $\mathrm{P}\mathrm{s}\ensuremath{-}\mathrm{A}\mathrm{r}$ systems were 1.55a0{1.55a}_{0}1.55a0​ and 1.79a0,{1.79a}_{0},1.79a0​, respectively. That there was only a 15% variation among the scattering lengths is compatible with the experiment of Coleman et al. [J. Phys. B 27, 981 (1994)], who found the low-energy cross sections for He, Ne, and Ar to be about the same size. The scattering lengths for Ps scattering from Li+,{\mathrm{Li}}^{+},Li+, Na+,{\mathrm{Na}}^{+},Na+, and K+{\mathrm{K}}^{+}K+ were 12.9a0,{12.9a}_{0},12.9a0​, 28.5a0,{28.5a}_{0},28.5a0​, and $\ensuremath{-}{1.9a}_{0}.$ The relatively small magnitude of the ${\mathrm{P}\mathrm{s}\ensuremath{-}\mathrm{K}}^{+}$ scattering length strongly supports previous suggestions that the ${\mathrm{P}\mathrm{s}\ensuremath{-}\mathrm{K}}^{+}$ system does not support a bound state. The annihilation parameter 1Zeff{}^{1}{Z}_{\mathrm{eff}}1Zeff​ has also been computed as part of the analysis. The present values of 1Zeff{}^{1}{Z}_{\mathrm{eff}}1Zeff​ are about 2.5--3 times smaller than the accepted experimental values since short-range electron-positron correlations were not taken into consideration when the annihilation matrix element was evaluated.
The scattering of orthopositronium from Kr and Xe is investigated with the fixed core stochastic variational method. The scattering lengths for Ps-Kr and Ps-Xe scattering in the fixed core approximation are 3.18a0{3.18a}_{0}3.18a0​ and 3.82a0,{3.82a}_{0},3.82a0​, respectively. Inclusion of core-polarization potentials leads to a significant reduction in the scattering lengths. The Ps-Kr and Ps-Xe scattering lengths were 1.98a0{1.98a}_{0}1.98a0​ and 2.29a0{2.29a}_{0}2.29a0​ for polarization potentials that were tuned to an average of the model electron-atom and positron-atom scattering lengths for the respective atoms. Other choices of the polarization potential resulted in scattering lengths that could be larger by 0.3a0{0.3a}_{0}0.3a0​ or smaller by 0.8a0.{0.8a}_{0}.0.8a0​. The pick-off annihilation parameter 1Zeff{}_{1}{Z}_{\mathrm{eff}}1​Zeff​ has also been computed as part of the analysis. The present values of 1Zeff{}_{1}{Z}_{\mathrm{eff}}1​Zeff​ are about 3 to 10 times smaller than the accepted experimental values since short-range electron-positron correlations were ignored when the annihilation matrix element was evaluated.
Electron-positron annihilation rates calculated directly from the electron and positron densities are known to underestimate the true annihilation rate. A correction factor, known as the enhancement factor, allows for the local increase of the electron density around the positron caused by the attractive electron-positron interaction. Enhancement factors are given for positrons annihilating with the 1s1s1s electron in H, He+{\mathrm{He}}^{+}He+, He, Li2+{\mathrm{Li}}^{2+}Li2+, and Li+{\mathrm{Li}}^{+}Li+. The enhancement factor for a free positron annihilating with He+{\mathrm{He}}^{+}He+ and He is found to be close to that of ortho-positronium (i.e., Ps in its triplet state) annihilating with these atoms. The enhancement factor for Ps-He scattering is used in conjunction with the known annihilation rate for pickoff annihilation to derive a scattering length of 1.47a01.47{a}_{0}1.47a0​ for Ps-He scattering. Further, enhancement factors for e+{e}^{+}e+-Ne and e+{e}^{+}e+-Ar annihilation are used in conjunction with the pickoff annihilation rate to estimate scattering lengths of 1.46a01.46{a}_{0}1.46a0​ for Ps-Ne scattering and 1.75a01.75{a}_{0}1.75a0​ for Ps-Ar scattering.
When positrons are injected into a gas, 75% of the positronium (Ps) is likely to be formed as long-lived ortho-Ps. The main decay mechanisms for the ortho-Ps have been assumed to be natural decay of ortho-Ps and pickoff annihilation of the positron during Ps-atom collisions. A third possibility for annihilation is $\mathrm{o}\mathrm{r}\mathrm{t}\mathrm{h}\mathrm{o}\mathrm{\text{\ensuremath{-}}}\mathrm{P}\mathrm{s}\ensuremath{\rightarrow}\mathrm{p}\mathrm{a}\mathrm{r}\mathrm{a}\mathrm{\text{\ensuremath{-}}}\mathrm{P}\mathrm{s}$ conversion due to the spin-orbit interaction between the atom and colliding Ps. This extra quenching mechanism may explain a number of phenomena observed in the annihilation spectrum of Kr and Xe, including the very small Ps fraction of 3% seen for Xe.
Abstract A single rearrangement collision between two spin-polarized orthopositronium beams leading to the production of either negative or positive positronium ions is studied. Negative or positive ions can be produced by the attachment of an electron or positron to a positronium atom, respectively. The probabilities for the formation of all possible spin states for both types of positronium ions are determined. The spin scattering matrix constructed using angular-momentum coupling as well as the spin density matrix containing the probabilities are given. The probabilities depend on the angle between the polarization vectors of the incoming beams and the real parts of complex scattering amplitudes labeled with total electron and total positron spin. We describe the effect of the spin alignment between the two beams on the probabilities and how the annihilation rates for ion decay and the real parts of the amplitudes can be obtained.