Krypton fine structure in perpendicular-plane electron-impact ionization

The dynamics of the outgoing electrons, from the separated fine-structure ionic states of the $4p$ valence shell of krypton atoms, are observed for the single ionization process by incident electrons with energies from 5 to 50 eV above threshold. Triple differential $(e,2e)$ ionization cross sections are deduced from observations made in the ``perpendicular-plane'' scattering geometry using the same toroidal electrostatic electron energy analyzer for both outgoing electrons. For equal energy outgoing electrons, single and double scattering mechanisms account for the major characteristics of the cross sections. The double scattering becoming increasingly dominant as the excess energy increases; the behavior otherwise is very different from helium.