Free positron annihilation in gases under the influence of a static electric field

Davies, S A; Charlton, M.; Griffith, T C

doi:10.1088/0953-4075/22/2/018

Cited by 7 publications

(17 citation statements)

References 33 publications

(54 reference statements)

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“…The present solutions gave a fit to the experimental data [2,7] that was significantly improved over previous simulations [7,10]. The variation of the equilibrium Z eff versus electric field strength has also been determined and again the agreement with experimental data was a significant improvement over previous calculations [9,10].…”

Section: Introductionsupporting

confidence: 66%

“…set is shown as are results from two previous transport calculations [7,10]. Experimental data from the University of Toronto [5], University of British Columbia (UBC) [55], and UCL [9] are presented. All calculated and experimental data show the same trend; there is a tendency for Z eff (E/n 0 ) to decrease as the reduced electric field E/n 0 is increased.…”

Section: B Positron Annihilation In Helium In An Electric Fieldmentioning

confidence: 99%

“…6. The MP cross-section [5], UBC [55], and UCL [9] laboratories. Previous transport calculations are also depicted [7,10]).…”

Section: B Positron Annihilation In Helium In An Electric Fieldmentioning

confidence: 99%

“…There are effectively four sets of experimental data: the data of the Toronto [5] and UBC [55] experiments, and the two UCL data sets [9] which were taken at densities of 3.5 and 35.7 amagat. The present MP Z eff (E/n 0 ) tends to lie higher than three of the experimental data sets.…”

Section: B Positron Annihilation In Helium In An Electric Fieldmentioning

confidence: 99%

“…The time-dependent behavior of Z eff for positrons annihilating in the rare gases has been extracted from the annihilation signal [2,[5][6][7][8]. Experimental information about the energy dependence of the positron-atom momentum transfer and annihilation cross sections can also be obtained by performing experiments in a static electric field [9]. The presence of the electric field leads to the drifting and diffusing positrons having a different energy distribution at equilibrium.…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Introductionsupporting

confidence: 66%

Section: B Positron Annihilation In Helium In An Electric Fieldmentioning

confidence: 99%

“…6. The MP cross-section [5], UBC [55], and UCL [9] laboratories. Previous transport calculations are also depicted [7,10]).…”

Section: B Positron Annihilation In Helium In An Electric Fieldmentioning

confidence: 99%

Section: B Positron Annihilation In Helium In An Electric Fieldmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

et al. 2014

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Positronium formation in the heavier noble gases in the presence of a static electric field

Charlton¹,

Cullen²,

Raza³

et al. 1992

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

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Under the gas pressure conditions of a positron lifetime experiment the behaviour of the fraction of positrons annihilating as long-lived ortho-positronium has been studied for argon, krypton and xenon under the influence of an applied static electric field. The ortho-positronium formation fraction is observed to rise in all gases with applied field and reaches a saturation level in argon and krypton. An anomalous field dependence of this fraction has been observed in xenon in which the initial rise is followed by a gradual decrease at higher fields and this is discussed in the light of previous work on positronium formation in this gas. In krypton and xenon the fast components which are visible at zero electric field are found to increase in amplitude when the field is raised. In the case of argon rapid annihilation components have been observed when the field is applied.

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Positron annihilation in liquid helium and liquid argon under an electric field

Pepe¹,

Paul²,

Steyaert³

et al. 1995

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

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We have made new measurements of the lifetimes at 4.29 K and 2.92 K in He I, and at 2.14 K and 1.67 K in He II, without and with an electric field. At 4.19 K we have a new value of the lifetime, 2.01+or-0.002 ns, leading to a Zeff of 3.53 at zero field. In contrast to earlier reports, Zeff decreases very slightly as the temperature is lowered and the density increases. The orthopositronium lifetime at 4.19 K is 98.1+or-0.2 ns, at zero field, independent of field up to 18 kV cm-1. At 4.19 K the free positron decay rate falls exponentially with increasing field to a value 5% below its zero-field value, the drop-off rate being 0.36+or-0.04 cm amagat V-1. From 28 through 50 V cm-1 amagat-1 the decay rate of the free component rises slowly as expected because of the increasing positronium fraction over the same range of electric field. In liquid argon there is positronium enhancement beginning at or below 3 V cm-1 amagat-1, which contrasts with 160 V cm-1 amagat-1 for argon gas. At least two lifetimes make up the long triplet component, suggesting different degrees of thermalization, or different states of positronium within the liquid. The effect of the electric field is to enhance the longer-lived, or more thermal component, in strong contrast with the findings of Charlton et al. (1992) for the gas. The argon results suggest positron behaviour similar to that of electrons in the liquid phase, namely, such particles move in a conduction band subject to small effective scattering and diffusion cross sections. An analytic model in which the scattering length is an adjustable parameter yields the onset of positronium enhancement just below 3 V cm-1 amagat-1 when as=-0.043 a0, corresponding to an elastic scattering and diffusion cross section of 0.034 pi a02. Consequences for positron thermalization are discussed. A model of positronium losing energy slowly in the liquid without bubble formation is suggested.

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Free positron annihilation in gases under the influence of a static electric field

Cited by 7 publications

References 33 publications

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

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

Positronium formation in the heavier noble gases in the presence of a static electric field

Positron annihilation in liquid helium and liquid argon under an electric field

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