Electron capture and ionization of 33-TeV Pb ions in gas targets

We have measured the total cross sections for electron capture by bare Pb⁸²⁺ ions and for the ionization of hydrogenlike Pb⁸¹⁺(1s) ions at 158GeV/A, γ=168, in Ar, Kr, and Xe gas targets. At this energy, the total capture cross sections are dominated by electron capture from pair production. The capture measurements are compared with the results of several theoretical calculations and with similar measurements made with solid targets. The Pb⁸¹⁺(1s) ionization cross sections obtained, which are substantially lower than those measured in solids, agree well with recent calculations that predict saturation at high energies from target screening effects.