Analytical transport cross section of medium energy positrons elastically scattered by complex atoms (Z=1–92)

Transport positron-atom elastic scattering cross sections have been computed for kinetic energies in the range 500–4000 eV. The phase shifts have been calculated by numerically solving the Dirac equation for a central electrostatic field up to a large radius in which the atomic potentials are negligible. Atomic potentials were that of Hartree–Fock for Z≤18 and of Dirac–Hartree–Fock–Slater for Z≳18. An analytical expression depending on three parameters, obtained by fitting the numerical results, is proposed for the energetic range examined to calculate transport cross sections for positron-atom elastic scattering in the atomic number range 1–92. The accuracy of the given expression for energies lower than 500 eV and greater than 4000 eV has been discussed by comparison with other tabulations.