Experimental aspects of the study of the interaction of low-energy positrons with gases

Griffith, T C; Heyland, G R

doi:10.1016/0370-1573(78)90127-8

Cited by 157 publications

(96 citation statements)

References 101 publications

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“…The experimental annihilation rates for the lighter noble gases are very well established (Coleman et al 1975, Canter and Roellig 1975, Griffith and Heyland 1978. Coleman et al (1975) measured the annihilation rates for all the noble-gas atoms.…”

Section: Introductionmentioning

confidence: 83%

Many-body calculations of positron scattering and annihilation from noble-gas atoms

Dzuba¹,

Flambaum²,

Gribakin³

et al. 1996

J. Phys. B: At. Mol. Opt. Phys.

106

164

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Abstract. We have applied many-body theory methods to study the interaction of low-energy positrons with noble-gas atoms. The positron-atom correlation potential includes explicitly the contribution from the target polarization by the positron and that from the virtual positronium (Ps) formation. It is demonstrated that the correlations and Ps formation (or tunnelling of electrons from the atom to the positron) create virtual levels in the positron-atom system. The existence of the virtual levels strongly influences the scattering and increases the positron annihilation rate by up to 400 times. The calculated elastic cross sections are in good agreement with experimental data. The inclusion of virtual Ps formation greatly improves the agreement with experimental annihilation rates with respect to calculations taking only the polarization into account. Our calculations have highlighted the difference between the calculation of positronatom scattering and the calculation of corresponding annihilation rates. The annihilation rate is very sensitive to the behaviour of the wavefunction at small positron-electron separations. A simple approximate formula based on the Sommerfeld factor is suggested to account for the effect of electron-positron Coulomb attraction on the annihilation rates.

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Section: Introductionmentioning

confidence: 83%

Many-body calculations of positron scattering and annihilation from noble-gas atoms

Dzuba¹,

Flambaum²,

Gribakin³

et al. 1996

J. Phys. B: At. Mol. Opt. Phys.

106

164

View full text Add to dashboard Cite

show abstract

“…In xenon the positron energy loss in momentum-transfer collisions is smaller due to the large mass of the atom, while the Z eff values in Xe are higher. As a result, the annihilation rate is measured for epithermal positrons, resulting in Z eff values lower than expected (e.g.,Z eff = 320 [77]). Adding small amounts of a lighter, low-Z eff gas, e.g., He or H 2 , to Xe allows for fast thermalization and produces truly thermalized annihilation rates withZ eff = 400-450 [76].…”

Section: B Thermally Averaged Z Effmentioning

confidence: 99%

Positron scattering and annihilation on noble-gas atoms

2014

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Positron scattering and annihilation on noble gas atoms is studied ab initio using many-body theory methods for positron energies below the positronium formation threshold. We show that in this energy range the many-body theory yields accurate numerical results and provides a nearcomplete understanding of the positron-noble-gas-atom system. It accounts for positron-atom and electron-positron correlations, including the polarization of the atom by the positron and the nonperturbative process of virtual positronium formation. These correlations have a large effect on the scattering dynamics and result in a strong enhancement of the annihilation rates compared to the independent-particle mean-field description. Computed elastic scattering cross sections are found to be in good agreement with recent experimental results and Kohn variational and convergent close-coupling calculations. The calculated values of the annihilation rate parameter Z eff (effective number of electrons participating in annihilation) rise steeply along the sequence of noble gas atoms due to the increasing strength of the correlation effects, and agree well with experimental data.

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“…When positrons are injected into an atomic or molecular gas, the result is a complex sequence of inelastic, elastic, and annihilating collisions [1,2]. The positrons slow down with inelastic collisions until the energy is sufficiently low that electronic excitations are no longer possible.…”

mentioning

confidence: 99%

“…During the collision processes, it is possible for the positron to capture an electron, forming positronium (Ps). Fast moving Ps can typically be expected to ionize, releasing the positron, but as the energy gets lower, it is possible for the Ps atoms to experience inelastic collisions with the gas, and therefore a portion of the positrons are trapped in the form of low energy Ps [1][2][3]. The Ps formed in the para(singlet)p-Ps state annihilates via the emission of 2 rays with an annihilation rate of 7:985 10 9 s ÿ1 .…”

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confidence: 99%

Spin-Orbit Quenching of Positronium during Atomic Collisions

Mitroy

Novikov

2003

Phys. Rev. Lett.

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When positrons are injected into a gas, 75% of the positronium (Ps) is likely to be formed as longlived 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 ortho-Ps ! para-Ps 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.

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Experimental aspects of the study of the interaction of low-energy positrons with gases

Cited by 157 publications

References 101 publications

Many-body calculations of positron scattering and annihilation from noble-gas atoms

Many-body calculations of positron scattering and annihilation from noble-gas atoms

Positron scattering and annihilation on noble-gas atoms

Spin-Orbit Quenching of Positronium during Atomic Collisions

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