Atomic collision processes in solids and gases at ultrarelativistic energies

At ultrarelativistic energies, we encounter unusual phenomena which control electron capture and loss and which contribute to the stopping power of io ns. Electron capture becomes dominated by capture from electron-positron pa irs, projectile-ionization cross-sections saturate as the "maximum" impact parameter exceeds the Thomas-Fermi radius of a neutral target atom and the stopping power is reduced when the wavelength of the target electron with r espect to the moving ion approaches nuclear size. (C) 2000 Elsevier Science B.V. All rights reserved.