Stopping Power of Gases for Lithium Ions

The molecular stopping powers of the bases ${\mathrm{H}}_2$, He, C${\mathrm{H}}_4$, ${\mathrm{N}}_2$, and C${\mathrm{O}}_2$ for lithium-6 ions in the kinetic-energy range 0.6 to 3.75 MeV have been measured to ±5%. The ratio of the molecular stopping powers for ${\mathrm{Li}}^6$ to previously known values for protons of equal velocity indicates that the effective charge of 3.75-MeV ${\mathrm{Li}}^6$ ions is 2.7 in ${\mathrm{H}}_2$ and 2.9 in C${\mathrm{O}}_2$. This indication from stopping powers is essentially the same as the effective beam charge obtained by Teplova et al. by magnetic analysis of a lithium beam which has passed through a celluloid foil; but at lower velocities magnetic analysis and stopping-power ratios do not give concordant estimates of the effective charge.