Positrons and Positronium in Gases

Fraser, P A

doi:10.1016/s0065-2199(08)60185-2

Cited by 110 publications

(33 citation statements)

References 80 publications

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“…It is found empirically that the value of Z eff at very low energies is proportional to the dipole polarizability α of the hydrogen atom (Osmon, 1965) [36] and can be represented by α 1.25 . The annihilation of positrons with electrons results in two photons at a rate λ, Fraser (1968) [37]: [19], D: Green and Gribakin (2013) [35]. In the above equation ρ is the density in grams per cubic centimeter and M A is the atomic mass.…”

Section: Z Effmentioning

confidence: 99%

Positron-Hydrogen Scattering, Annihilation, and Positronium Formation

Bhatia

2016

Atoms

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Abstract:In previous papers (Bhatia A.K. 2007, 2012) a hybrid theory for the scattering of electrons from a hydrogenic system was developed and applied to calculate scattering phase shifts, Feshbach resonances, and photoabsorption processes. This approach is now being applied to the scattering of positrons from hydrogen atoms. Very accurate phase shifts, using the Feshbach projection operator formalism, were calculated previously (Bhatia A.K. et al. 1971 and Bhatia et al. 1974a). The present results, obtained using shorter expansions in the correlation function, along with long-range correlations in the Schrödinger equation, agree very well with the results obtained earlier. The scattering length is also calculated and the present results are compared with the previous results. Annihilation cross-sections, and positronium formation cross-sections, calculated in the distorted-wave approximation, are also presented.

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Section: Z Effmentioning

confidence: 99%

Positron-Hydrogen Scattering, Annihilation, and Positronium Formation

Bhatia

2016

Atoms

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“…Besides reproducing the low-energy elastic cross section, this model potential approach also does a reasonable job of reproducing Z eff (v). The annihilation parameter is computed from the scattering wave function using [4,25,26] …”

Section: Collision Modelmentioning

confidence: 99%

“…One parameter is the positronium fraction, i.e., the number of positrons surviving in the form of free positronium. Another parameter is the annihilation parameter, Z eff (v), which can be defined in terms of the spin-averaged annihilation cross section, σ ann (v), by the identity [4],…”

Section: Introductionmentioning

confidence: 99%

Transport theory for low-energy positron thermalization and annihilation in helium

et al. 2014

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A transport theory that explicitly incorporates loss of flux due to annihilating collisions is developed and applied to low-energy positron diffusion and annihilation. The use of more complete momentum transfer and annihilation cross sections for helium has resulted in improved descriptions of the time dependence of Z eff for positrons injected into gaseous helium. Similarly, the variation of Z eff versus E/n 0 for experiments where the annihilation region is immersed in an electric field is in closer agreement with experimental data. Inclusion of loss of flux due to annihilation was found to have a very small effect on the derived Z eff (t) for helium.

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“…The annihilation parameter Z eff is computed from the scattering wave function using the identity [23][24][25],…”

Section: G Positron Annihilationmentioning

confidence: 99%

Stochastic variational calculation of zero-energy positron scattering from H, He, andH2

Zhang

Mitroy

2011

Phys. Rev. A

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The confined variational method is used to generate a set of energy-optimized explicitly correlated Gaussians to describe positrons interacting with H, He and the H 2 molecule. These basis functions are then used in a Kohn variational calculation of the scattering lengths and zero-energy annihilation parameters, Z eff . The results for the H and He atoms are consistent with previous high-quality variational calculations while the annihilation parameter for H 2 is consistent with experiment. An extensive tabulation of the H 2 scattering parameters as a function of internuclear distance confirm the existence of a virtual state at R ≈ 3.4a 0 . The scattering length was −2.71a 0 and Z eff was 15.7 at the mean H 2 internuclear distance of 1.45a 0 .

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Positrons and Positronium in Gases

Cited by 110 publications

References 80 publications

Positron-Hydrogen Scattering, Annihilation, and Positronium Formation

Positron-Hydrogen Scattering, Annihilation, and Positronium Formation

Transport theory for low-energy positron thermalization and annihilation in helium

Stochastic variational calculation of zero-energy positron scattering from H, He, andH2

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