PRODUCTION AND TRAPPING OF HYDROGENLIKE AND BARE URANIUM IONS IN AN ELECTRON-BEAM ION-TRAP

An equilibrium population of approximately 500 hydrogenlike U91+ ions and ten fully stripped U92+ ions has been produced and trapped in an electron beam ion trap at 198-keV electron energy. The equilibrium ionization balance, determined from the intensities of radiative recombination x rays, gives values of 1.55 +/- 0.27 and 2.82 +/- 0.35 b for the electron impact ionization cross sections of hydrogenlike and heliumlike uranium, respectively. These values are somewhat larger than relativistic distorted wave calculations, and much smaller than previous values inferred from stripping of accelerator beams.