Positron scattering from atoms and molecules using a magnetized beam

Sullivan, James P.; Gilbert, S. J.; Marler, Joan; Greaves, R. G.; Buckman, Stephen; Surko, C. M.

doi:10.1103/physreva.66.042708

Cited by 103 publications

(152 citation statements)

References 50 publications

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“…Those that are transmitted by the RPA then encounter a double-stack, microchannel-plate detector. In a collision with a target gas atom, the positron can be scattered through some angle θ , in the process losing some E || , and it can also lose some of its total energy if inelastic processes are energetically allowed [17]. Ps formation is also possible above the Ps formation threshold E Ps , corresponding to 7.200 eV for Kr, and results directly in a loss of positrons from the beam.…”

Section: Methodsmentioning

confidence: 99%

“…The techniques that have been used for the measurements of total scattering and total Ps formation cross sections have been presented in a recent paper [18] and previous work [17] and will not be repeated in detail here. The technique involves the measurement of a number of transmitted positron intensities at various values of the potential applied to the RPA.…”

Section: A Total Cross Sectionsmentioning

confidence: 99%

“…Our technique, described in detail in [18], relies on measuring the transmitted positron intensity at the beam cutoff point on the retarding potential analyzer voltage axis (see Refs. [17,18] for full details on this technique). In practice, however, it is not possible to make a measurement of the intensity at exactly the cutoff voltage because this also coincides with the cutoff point of the primary positron beam.…”

Section: A Total Cross Sectionsmentioning

confidence: 99%

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Low-energy positron interactions with krypton

et al. 2011

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Section: Methodsmentioning

confidence: 99%

Section: A Total Cross Sectionsmentioning

confidence: 99%

Section: A Total Cross Sectionsmentioning

confidence: 99%

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Low-energy positron interactions with krypton

et al. 2011

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“…It allows one to derive the TCS from a knowledge of attenuation measurements of the beam intensity, the target pressure in the scattering cell and the length of the interaction region. The methods used in the present experiment to measure the TCS and the Ps formation cross sections are based on the principles of positron motion and scattering in a strong magnetic field 25 and have been previously presented, as well as our data analysis techniques. 26 Briefly, the cross sections are determined by measuring specific fractions of the positron beam transmitted through the RPA with the target vapor present in the scattering cell.…”

Section: Methodsmentioning

confidence: 99%

Experimental and theoretical cross sections for positron collisions with 3-hydroxy-tetrahydrofuran

Chiari

Palihawadana

Machacek

et al. 2013

The Journal of Chemical Physics

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Cross section results from a joint experimental and theoretical investigation into positron scattering from 3-hydroxy-tetrahydrofuran (3H-THF) are presented. Total and positronium (Ps) formation cross sections have been measured from 1 to 190 eV using the positron beamline at the Australian National University, which has an energy resolution between 60 and 100 meV. The total cross section (TCS) and the elastic and total inelastic integral cross sections in the energy range between 1 and 1000 eV have been computed within the Independent Atom Model using the Screening Corrected Additivity Rule approach. In addition, we have calculated elastic differential cross sections at selected incident energies. Our computations represent the first theoretical results reported for this target species, while our measured Ps formation cross sections are also novel. Comparison of the present TCS with the previous results from the University of Trento shows a good level of agreement at the lowest energies. We also provide a comparison between the present cross sections for 3H-THF and those from our earlier study on the parent molecule tetrahydrofuran.

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“…This allows us to extend the MERT applicability for positrons to energies above 1 eV. A clear indication on importance of p-wave scattering in this energy range comes from recent differential cross sections measurements in argon [19]. The present model introduces a second MERT parameter for the p-wave shift thus developing an approximation with two parameters for both s and p-wave phaseshifts.…”

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confidence: 99%

Applicability of modified effective-range theory to positron-atom and positron-molecule scattering

Idziaszek

Karwasz²

2006

Phys. Rev. A

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We analyze low-energy scattering of positrons on Ar atoms and N2 molecules using Modified Effective-Range Theory (MERT) developped by O'Malley, Spruch and Rosenberg [Journal of Math. Phys. 2, 491 (1961)]. We use formulation of MERT based on exact solutions of Schrödinger equation with polarization potential rather than low-energy expansions of phase shifts into momentum series. We show that MERT describes well experimental data, provided that effective-range expansion is performed both for s-and p-wave scattering, which dominate in the considered regime of positron energies (0.4 -2 eV). We estimate the values of the s-wave scattering lenght and the effective range for e + -Ar and e + -N2 collisions.Electron (and positron) scattering on atoms at very low energies is dominated by polarization forces. Applicability of MERT to low-energy positron scattering was already hypothesized in [2]. However, first measurements of total cross sections for positron scattering at low energies on noble atoms come only from seventies [10,11].The most systematic data for noble atoms, extending down to 0.3 eV were done in WSU Detroit lab, using positrons from a short-lived C 11 radionuclid, with about 0.1 eV energy resolution [11]. Those data indicated clearly a rise of the cross section in the zero energy limit in gases, like He, Ar, H 2 , Kr, Xe, CO 2 , see [11]. Unfortunately, subsequent experiments [12, 13] used Ne 22 source and thick W-vanes positron moderator, thus worsening energy resolution and not allowing to make reliable measurements below 1 eV. To gain in signal, large apertures and strong guiding magnetic fields were used, leading to underestimation of cross sections -some data showed even a fall in the limit of zero energy for highly polarizable targets, like C 6 H 6 [14].Only two of the most recent set-ups reached energies below 1 eV with good signal-to-noise ratio. In San Diego annihilation rates in Ar and Xe were measured, showing a steep rise below 1 eV [15]. In Trento total cross sections in Ar and N 2 were measured [16] with angular resolution better by a factor of 30 than in some previous experiments [12]. Both laboratories confirm the early observations from WSU Detroit on the rise of positron cross sections in the zero-energy limit. Such a rise is also predicted by ab-initio theories [17], see [16] for detailed comparison. A phenomenological attempt to apply MERT-like fit for low-energy cross sections in benzene and cyclohexane was done by Karwasz, Pliszka and Zecca [18].In the present paper we apply MERT to positron total cross sections on argon and nitrogen, using recent experimental data from Trento [16]. We use MERT model based on direct solution of Schrödinger equation with polarization potential as originally proposed by O'Malley, Spruch and Rosenberg [1]. Differently from earlier works, for the p-wave phaseshift we consider not only the polarization potential but contribution from a general-type short range interaction. This allows us to extend the MERT applicability for positrons to energies above 1 e...

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Positron scattering from atoms and molecules using a magnetized beam

Cited by 103 publications

References 50 publications

Low-energy positron interactions with krypton

Low-energy positron interactions with krypton

Experimental and theoretical cross sections for positron collisions with 3-hydroxy-tetrahydrofuran

Applicability of modified effective-range theory to positron-atom and positron-molecule scattering

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