Positron- (and Electron-) Alkali Atom Total Scattering Measurements
From the outset of scattering experiments with low energy positron beams, there has been a natural tendency to make comparisons between the scattering of positrons and electrons by the same target atoms and molecules. Since positrons, being the antiparticles of electrons, have the same magnitudes for the mass, charge, and spin as the electron, but have the opposite sign of charge, comparison measurements of the scattering of positrons and electrons by atoms and molecules can reveal interesting differences and similarities that arise from the basic interactions which contribute to scattering. The exchange interaction contributes to electron scattering (due to the indistinguishability of the projectile and electrons in the target atoms) but does not play a role in positron scattering. The static interaction (associated with the interaction of the projectile with the Coulomb field of the undistorted atom) is attractive for the electron and repulsive for the positron, while the polarization interaction (resulting from the distortion of the atom by the charged projectile) is attractive for both projectiles. The net effect of the static and polarization interactions is that they add to each other in electron scattering whereas they tend to cancel each other in positron scattering. In general, this results in smaller total scattering cross sections (QT’s) for positrons than for electrons at low energies.
KeywordsPotential Curf Alkali Atom Projectile Energy Alkali Metal Atom Positron Energy
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