Production of Ultrahigh Charge States in Heavy-Ion Collisions

Charge-state fractions have been determined for iodine, selenium, and bromine ions traversing oxygen, argon, krypton, xenon, carbon-foil, and gold-foil targets. Particular attention has been paid to high charge states, some containing as little as 10^-6% of the primary beam intensity. Despite the fact that heavy-gas targets produce a low mean charge, they were found to be more efficient producers of very high charge states than lighter targets. For the very highest charge states record (> 22+ for iodine ions at 12 MeV), the heaviest gas target Xe produced even more of these ions than a carbon foil. Measurements of the attenuation cross section and scattering for the ultrahigh charge states are also reported.