Ionization of uranium atoms by electron impact

The cross sections for single and multiple ionization of uranium by electron impact for energies 7.5-500 eV have been measured using a modulated crossed-beam experiment. The absolute total ionization cross section was found by comparing the cross section for ionization to the cross section for associative ionization in the reaction U+${\mathrm{O}}_2$→U${\mathrm{O}}_2^{+}$+$e$. The total ion number cross section has a maximum value of (5.8±0.9)×${10}^{-16\mathrm{}}$ ${\mathrm{cm}}^2$ occurring at an energy of about 50 eV. The single ionization cross section has a maximum of (4.80±1.24)×${10}^{-16\mathrm{}}$ ${\mathrm{cm}}^2$ at an energy of 27±5 eV. The cross sections for higher-order ionization have values at 500 eV that are 49%, 33%, and 17% that of single ionization for $n=2, 3, \mathrm{and} 4$, respectively. These ratios are significantly higher than those for other elements for which data are available.