Positron - Hydrogen Scattering at Intermediate Energies

Abstract

Calculations of positron-hydrogen scattering at intermediate energies up to a maximum energy of 10 Ryd are performed using the close coupling (CC) approach. A large L2 basis of positron-hydrogen channels (28 states) is supplemented by the Ps(1s), Ps(2s) and Ps(2p) channels. The inclusion of the positronium states in the CC expansion leads to a model which can describe most of the physics of the positron-hydrogen system with a reasonable degree of accuracy. In particular, the positronium formation cross section, the total reaction cross section and the ionisation cross section are all in agreement with experiment. The elastic scattering cross section and the cross sections for positron impact excitation of the H(2s) and H(2p) levels are also reported.

The structure of exotic atoms containing positrons and positronium

“…The energy of −0.752 5 Hartree was comparable to the energy of −0.752 51 Hartree reported in the original calculation of Ore [10]. A similar tendency for slow convergence of the phase shift has been noticed in standard close-coupling calculations (without positronium channels) of positron-hydrogen scattering [86][87][88].…”

Recommended Positron Scattering Cross Sections for Atomic Systems

“…In the late 1990s, Ratnavelu and Rajagopal [74] demonstrated an optical potential method (CCO(m,n)), within the CC two-centre formalism of Mitroy [37], that allowed for the continuum optical potentials in the positron-atom channels. Using a small basis calculation (CC (3,3) and CCO(3,3)), they reported ionization cross sections, Ps formation cross sections and total cross sections that were in good qualitative and reasonable quantitative agreement with the 31-state CC calculations of Mitroy [75] and the 33-state R-matrix calculations of Kernoghan et. al [76].…”

“…These later results from the Bielefeld/Brookhaven collaboration are in good agreement with the results of the UCL group [154], which were undertaken primarily to validate the earlier measurements of [153], which were considerably larger than most contemporary theoretical calculations of the ionization process. Given the good agreement between the results of [152] and [154], and between these results and contemporary theory [58,75,76], our recommended cross section is largely based around these data. The cross sections are tabulated in Table 4.1.3 and shown in Figure 4.1.3, with an estimated uncertainty of ±25%.…”

“…While there are no other experimental values with which to compare, when compared (see e.g. [16]) with several state-of-the-art theoretical approaches [56,75,95,142,155] the agreement between experiment and theory is excellent at energies above about 8 eV. The Wayne state group discuss possible forward scattering effects in their measured cross sections, and provide estimates of the extent that these may effect the measured cross sections.…”

Antihydrogen from positronium impact with cold antiprotons: a Monte Carlo simulation

“…This accuracy was confirmed by the excellent agreement of the CC(13, 8) model calculations of positron-hydrogen scattering [26] with the latest variational calculations [28]. The cross sections at incident positronium energies larger than 6.8 eV are taken from CC(28, 3) model calculations [23,24] in which a large L 2 basis of positron-hydrogen channels (28 s-, p-and d-states) supplemented by the positronium (1s, 2s and 2p) states was used. These cross sections reproduce existing ionization and positronium formation cross sections and are consistent with a similar large-scale close-coupling calculation using the R-matrix method [29].…”