Electron Impact Ionization ofU88+-U91+

We channeled 405-MeV/nucleon uranium ions in Si single crystals to determine the electron impact ionization cross section for berylliumlike-hydrogenlike uranium by 222-keV electrons, Our cross sections are 3.9, 11.0, 16.0, and 31.0 b (+100%, -50%), respectively, for ionizing $1s$, ${1s}^2$, $2s$, and ${2s}^2$ electrons. Our $1s$ and ${1s}^2$ results disagree with present theory. Our $2s$ and ${2s}^2$ results are not accurate enough to distinguish between theories.