Ab initio optical potentials for elastic electron and positron scattering from the heavy noble gases

We have derived a non-local, complex and ab initio absorption potential within the framework of the relativistic Dirac scattering equations and applied it to elastic scattering of electrons and positrons from the heavy noble gases. We have also developed a perturbation method based on the Hulthen-Kato formalism that enables us to calculate the scattering phase shifts using only real quantities and with a very significant reduction in computational effort. We have used this method to calculate differential cross sections and spin asymmetry parameters for the elastic scattering of electrons from krypton. In addition, we have applied this method to the elastic scattering of positrons from krypton. Our results are compared to experimental measurements and substantial improvements are obtained at intermediate energies with respect to calculations either without an absorption potential or with a semi-empirical absorption potential.