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+O₂{→}UO₂⁺+e. The total ion number cross section has a maximum value of (5.8±{}0.9)×{}10^-16 cm² occurring at an energy of about 50 eV. The single ionization cross section has a maximum of (4.80±{}1.24)×{}10^-16 cm² 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, and 4, respectively. These ratios are significantly higher than those for other elements for which data are available.