CHARGE-DEPENDENT ELECTRONIC STOPPING OF SWIFT NONRELATIVISTIC HEAVY-IONS

The stopping of swift nonrelativistic heavy ions has been analyzed the oretically as a function of the projectile charge q(1). Excitation and ionization of target electrons are described within Bohr's classical theory and the limitations toward Bethe's quantal description are outl ined. For oxygen ions in carbon the Bethe regime is found to be confin ed to the velocity range where the ion is essentially stripped in char ge equilibrium. The effect of projectile electrons is taken into accou nt mainly via screening of the Coulomb interaction, but excitation of projectile electrons is discussed briefly. The significance of project ile screening hinges on a parameter s that parameters and varies subst antially over the electron shells of the target. Calculated fixed-char ge stopping cross sections agree well with measured values in absolute magnitude and in their variation with charge state. q(1)(2) scaling f requently has been assumed in the literature. A continuous transition is predicted between such scaling and a stopping power that is almost independent of the projectile charge.