Helium 4 High energy physics 4 Isoelectronic series 4 Angular expansions 2 Asymptotic analysis 2 Born approximation 2 Boundary conditions 2 Charged ions 2 Continuum distorted waves 2 Critical nuclear charge 2 Cross sections 2 Distortion (waves) 2 Eikonal 2 Electric power plants 2 Electrolysis 2 Electron atoms 2 Electron yields 2 First Born approximations 2 First orders 2 Harmonic analysis 2 Impact ionization 2 Initial states 2 Insulator surfaces 2 Ionization 2 Ionization cross sections 2 Krypton 2 Lithium 2 Mathematical models 2 N-electron atoms 2 Neon 2