Measurement of total cross sections (e⁺, Ne) and (e⁺, Ar)

Abstract

The total cross sections for positrons on neon and argon atoms have been measured in the energy ranges 15 eV to 272.5 eV and 25 eV to 300 eV respectively. The cross sections indicate clearly that Born values will not be reached until at least 3 KeV. Interpolating between the measured and the valid Born regions has allowed an application of the sum rule which connects scattering length. Born forward scattering amplitude, and the momentum-integral over the total cross section. This procedure gives scattering lengths as = −0.53 ± 0.15 Bohr radii for neon and as = −2.8 ± 0.7 Bohr radii for argon; the errors include maximum credible uncertainties in the interpolations.

Positron scattering from argon: total cross sections and the scattering length

“…The Trento University spectrometer was developed by Zecca and colleagues and has been described previously many times (see for example [24,25]). We therefore do not repeat those details again, except to note that a tungsten moderator of thickness 1 μm [26] was employed in conjunction with a radioactive 22 Na isotope (current activity ∼1.5 mCi) and some electrostatic optics in order to produce the positron beam. These optics were originally designed to produce a stable and well-focused (into the scattering cell) positron beam with energies between ∼0.1 and 50 eV [25].…”

Recommended Positron Scattering Cross Sections for Atomic Systems

“…There have been many studies of positron scattering from neon (Ne), with measurements of the total cross section [65,161,162,165,[169][170][171][172][173][200][201][202][203][204][205], the positronium formation cross section [65,182,185,[206][207][208][209], and the direct ionization cross section [26,189,191,192,208,[210][211][212][213] having been reported. We also note several measurements [207,208,214] of the total ionisation cross section (direct ionization + positronium formation), and a measurement of the direct double ionization cross section [215].…”

“…Positron scattering from argon (Ar) has possibly received more experimental and theoretical attention than any of the other heavy rare gas atoms, no doubt due to the ready availability and use of argon as a target gas. There have been a large number of total scattering cross section measurements [65,161,162,165,[171][172][173][200][201][202]204,[251][252][253][254], as well as measurements of the positronium formation cross section [65,181,182,185,[207][208][209]236,[255][256][257][258], electronic excitation [8] and the direct ionization cross section [189,[191][192][193]210,211,213]. There have also been a considerable number of theoretical calculations of these various processes [65,97,100,126,128,129,197,216,218,…”

Positron scattering and ionization of neon atoms — theoretical investigations

“…Also the mea-sured values given in Refs. [2] and [3] differ in a range of 30-40 eV. The corresponding theoretical calculations of Q T were carried out in Refs.…”