Recommended Positron Scattering Cross Sections for Atomic Systems

Abstract

We present a critical analysis of available experimental and theoretical cross section data for positron scattering from atomic systems. From this analysis we present (where data is available) recommended cross sections for total scattering, positronium formation, inelastic scattering and direct ionization processes. A complete bibliography of available measurement and theory is also presented.

Positron Scattering from Gas-Phase Beryllium and Magnesium: Theory, Recommended Cross Sections, and Transport Simulations

“…6(d) is that both our OP and ROP calculations predict the positronium formation cross section to persist to somewhat higher energies than that found in the 2-center CCC result. 12 In the case of He, the eigen 2-electron system (both Be and Mg can be considered as quasi-2electron systems 22,23 ), Ratnavelu et al 2 recommended a positronium formation cross section, based on measurements, that persists out to about 200 eV. This energy range in He is more consistent, in this case, with the present OP and ROP computations than that from the CCC for Mg: In Fig.…”

“…In this case, however, at the TCS level [ Fig. 6(e)], we at least have experimental results from the Wayne State University group [7][8][9] which are embodied in the recommended data from Ratnavelu et al 2 That data predicts a strong low-energy resonance feature, which is well reproduced by the theoretical results from the computations of Poveda et al, 6 Mitroy et al, 10 and the CCC 12 but not by our ROP or the results of Bromley et al 3 Indeed, to within the ±20% data uncertainty cited by Ratnavelu et al, 2 the level of accord between their recommended data and the CCC, over the common energy regime, is excellent [see Fig. 6(e)].…”

“…Let us now consider Mg. Remembering that below the positronium formation threshold energy the total cross section is equivalent to the elastic ICS, the recommended TCS of Ratnavelu et al 2 provides a guide to its elastic ICS below E Ps . That comparison suggests that the CCC elastic ICS is quantitatively reproducing this cross section at lower energies.…”

“…In regard to positron-Mg scattering, experimental data, largely from the group that was based at Wayne State University, can be found in the literature. 7,8 Most of that data relates to the TCS, although a preliminary result for the positronium formation ICS was published in the work of Surdutovich et al 9 However, in their review, Ratnavelu et al 2 declined to use that preliminary data in order to form a recommended positronium formation cross section and as a consequence we do not consider it further. Similar to that just described above for Be, theoretical elastic ICSs for positron-Mg scattering are also available from Bromley et al, 3 Mitroy and Ivanov, 4 Reid and Wadehra, 5 and Poveda et al 6 In this case, those elastic ICSs equate to the TCS below 0.846 eV, the positronium formation threshold energy of Mg.…”

Positron Impact Excitation of the 2S State of Atomic Hydrogen

“…They find excitation cross-sections increase in a linear manner as the incident energy is increased from the threshold to 1 Ry. Calculations have been carried out by Ratnavelu et al [8] to obtain total cross-sections: elastic scattering, positronium formation, and ionization cross sections. Total cross-sections must include excitation to higher levels.…”