Positron scattering from rare gases (He, Ne, Ar, Kr, Xe, and Rn): Total cross sections at intermediate and high energies

Abstract

The total (elastic plus inelastic) cross sections for positron scattering from all the rare gases are reported at intermediate and high energies (20-1000 eV), where experimental data are available for comparison except for the case of radon gas. A complex-optical-potential [ V,~, (ri] approach is employed in which the real part (static plus polarization terms) is calculated from Hartree-Fock or Dirac-Hartree-Fock target wave functions. The imaginary part of the optical potential, i.e. , the absorption potential [ V,b, (r}],is derived for each gas semiempirically from the corresponding electron absorption potential (r}] in the form of V+~, (r}= f (k, r}V, b, (r}, where f (k, r} depends on the incident energy (k') and radial distance (r). The V,b, is taken from the work of Truhlar and co-workers. The V,~, (r) is treated exactly in a partial-wave analysis under the variable-phase method. With the present form of V,~,(r), we are able to reproduce experimental 0, values at all energies considered here. An additional feature of the present results is that the inelastic cross sections compare very well with the measured inelastic (sum of positronium formation, excitation, and ionization cross sections) values for rare gases, where such experimental data are available. The 0. , for the positron-Rn system are predicted. We also discuss the correlation between scattering cross section and the atomic properties. We found that at intermediate and high energies, the positron-gas total cross section can be represented by an analytic formula o, (10 ' cm') =21. 16+aoia03}/EieV}, where ao is the target polarizability and E is the impact energy.This simple form of the o. , in terms of target polarizability works very well for highly polarizable targets such as the alkali-metal atoms and several hydrocarbon molecules. In particular, by using the above analytic formula for 0 "we have shown that our results for Na, K, Rb, C&H4, C,H6, and C3H6 targets compare very well with the experimental data. PACS number(s): 34.80.i, 34.90.+ q, 61.80.Fe

Low-energy positron interactions with krypton

“…Qualitative agreement is also observed with a number of previous results, and good overall agreement is found with the preliminary data of [34], albeit with the present values being higher over all the energy range of overlap. Good agreement is observed with the results of [1] at energies above 30 eV, while there are significant energy dependence and magnitude differences between the present results and those of [2]. Significant differences are also observed between the present σ GT -σ Ps and most literature values.…”

“…This problem has now been solved by new CCC formulations for helium [24], and work is currently ongoing to extend the two-center technique to the heavier noble gases. Good agreement between the present experimental results and the earlier theoretical results of Baluja and Jain [1] is noted above 30 eV. However, their calculated cross section differs from both our experimental and calculated cross sections, as it rather 032721-5 [36] and ionization cross sections of Campeanu et al [37][38][39].…”

“…This earlier work and the theoretical calculations for Kr up until 1992 have been well summarized by Baluja and Jain [1]. Thereafter, the only work on σ GT has been a more recent theoretical calculation by Parcell et al [2].…”

Elastic Positron Scattering from Krypton and Xenon in the Relativistic Polarized Orbital Approximation

“…Wadehraet al [18] predicted existence of a critical point in the angular distribution of elastically scattered slow positrons. Moreover, Baluja and Jain [21] presented results of their calculations of the total (elastic plus inelastic) cross-sections in the energy range 20-1000 eV and McAlinden and Walters [20] reported cross-sections for positronium formation.…”

“…Moreover, Schultz et a1. [19] and McAhinden (309) and Walters [20] carried out calculations of the positronium formation cross-section while Baluja and Jain [21] reported the total (elastic plus inelastic) cross-sections at intermediate and high energies.…”