Elastic scattering of electrons and positrons from alkali atoms

Abstract

This review comprises the recent investigations on the elastic collisions of electrons and positrons with alkali metal atoms ( 7 Li, 23 Na, 39 K, 85 Rb, and 133 Cs). Differential, integrated, and total cross sections are presented in the energy range from 10 eV to 500 MeV. A detailed analysis of the critical minima in the differential cross sections along with the positions of the corresponding maximum polarization points in the Sherman function is also provided. In order to cover such a wide energy range for these scattering observables, two different theoretical approaches are employed: (i) the relativistic Dirac partial wave (phase-shift) analysis using a complex optical-potential model (OPM) and (ii) the nuclear structure approach (NSA). The OPM incorporates the interactions of the incident lepton with both the nucleus and the bound electrons of the target atom. The NSA retains only the lepton–nucleus interaction while considering higher multipoles within the distorted-wave approximation. A systematic investigation for obtaining an overlap region within the two models is made for establishing a bridge to connect appropriately the low- and high-energy results. Presented are also detailed studies of the spin asymmetry, sensitive to phases related to interference effects which are caused by the different constituents of the lepton–atom or lepton–nucleus interactions. A compilation of the existing experimental and theoretical results on this subject is furnished. The comparison with these data demonstrates the power of the present approach to explain the measurements except in the very low energy domain. For the integrated (momentum transfer and viscosity) cross sections a scaling with charge number Z T 1.9 is discovered for collision energies between 10 keV and 10 MeV. Also the magnitude of the spin asymmetry as well as its Z T -dependence is found to be fundamentally different for positron as compared to electron impact scattering at low and intermediate energies. The present OPM theory is simple enough to be universally applicable to any element of the periodic table without any cumbersome numerical efforts.