Equilibrium Charge-State Distributions of 2-15-MeV Tantalum and Uranium Ions Stripped in Gases and Solids

Equilibrium charge-state fractions have been measured for tantalum and uranium ions with energies of 2, 4, 6, 8, 10, and 15 MeV, stripped in ${\mathrm{H}}_2$, He, ${\mathrm{N}}_2$, ${\mathrm{O}}_2$, Ar, Kr, Xe, carbon, and gold. Average charge and form of the charge distributions and the dependence on ion velocity and target species are discussed. The results on the average charge are compared with theoretical and semiempirical predictions. An anomaly has been found in the particular case of helium targets in which certain charge-state fractions are of unusual magnitude, leading to a relatively high average charge.