K-Shell Ionization Cross Sections for 2.04-MeV Electrons

$K$-shell ionization cross sections have been measured at 2.04-MeV incident electron energy for 32 elements from V ($Z=23\mathrm{}$) to Bi ($Z=83\mathrm{}$). Measured cross sections drop from a value of 353 b at V to 9.9 b at Bi. The general trend of the $Z$ dependence of the cross sections is in agreement with theoretical predictions of Kolbenstvedt. However, variations in cross sections by as much as 30% from one element to the next are not accounted for by the theory.