Influence of ionic charge state on the stopping power of 27.8- and 40-MeV oxygen ions in the [011] channel of silver

In many cases, it has been assumed that the stopping power of an ion is not strongly influenced by its ionic charge because screening electrons would largely mask the effect of charge-state differences. Usually it is difficult to tell whether an ion moving through a solid is highly stripped but highly screened or less highly stripped and screened. Earlier experiments had demonstrated that fast prestripped oxygen ions are able to survive passage through crystal channels of ∼ 1-μm length and more without electron capture or loss. An experiment to detect slight differences in screening which would cause small differences in the stopping powers of ${\mathrm{O}}^{8+}$, ${\mathrm{O}}^{7+}$, and ${\mathrm{O}}^{6+}$ ions has been performed with 27.8- and 40-Mev O ions in the [011] channel of a Ag crystal with 0.8-μm pathlength. The differences are not small. The stopping powers follow the simple relation $S={\mathrm{kq}}^2$. The result in this case indicates that dynamic screening by conduction electrons plays no significant role in equalizing stopping powers.