Ionization 20 Continuum distorted wave-eikonal initial state 18 Distortion (waves) 16 High energy physics 14 Multiple ionization 12 Atoms 10 Impact ionization 10 First Born approximation 8 Protons 8 Charge density waves 6 Helium 6 Ionization cross section 6 Ionization of gases 6 Proton impact 6 Approximation theory 4 Branching ratio 4 CDW-EIS 4 Calculations 4 Collisional contributions 4 Energy ranges 4 Inert gases 4 Inner-shell ionization 4 Intermediate energies 4 Ions 4 Projectiles 4 Proton 4 Shells (structures) 4 Single ionization 4 Theoretical study 4 Total ionization cross sections 4