Relativistic positron scattering from heavy ground-state nuclei

TL;DR

This paper presents relativistic calculations of positron scattering and bremsstrahlung emission from heavy nuclei, comparing results with electron scattering and analyzing spin asymmetries and cross sections at various energies.

Contribution

It provides the first detailed relativistic partial-wave analysis of positron scattering and bremsstrahlung, highlighting differences from electron scattering and effects of magnetic interactions.

Findings

Positron and electron scattering intensities converge at high energies.

Magnetic scattering significantly reduces spin asymmetries.

Bremsstrahlung cross section increases with photon frequency at certain angles.

Abstract

Cross sections and spin asymmetries for elastic positron scattering and for the emission of positron bremsstrahlung in collision with nuclei of zero and half-integer spin are calculated within the relativistic partial-wave theory. For elastic scattering, comparison is made with the respective results from electron scattering by 208Pb, 89Y and 23Na nuclei at high energies (up to 400 MeV). It is found that the difference between electron and positron intensities diminishes with energy, although the diffraction oscillations, which differ in phase for the two species, prevail up to the highest energies considered. Magnetic scattering strongly reduces the spin asymmetries for nuclei with spin, both for positrons and electrons. For the elementary process of bremsstrahlung the cross section, which is studied for the 197Au and 208Pb targets at low energies (1-30 MeV), increases with photon frequency for large scattering angles and small photon emission angles, in contrast to the usual behaviour of the doubly differential cross section, or of the triply differential cross section at small scattering angles.