Cross Sections for K -Shell Ionization by 2-MeV-Electron Impact

A systematic study of the cross sections for K-shell ionization by 2.0-MeV-electron impact has been made as a function of atomic number. The cross sections for 32 elements from V ($Z=23$) to Bi ($Z=83$) were first measured relative to each other, and then were normalized to 43 b at Sn ($Z=50$). Thus systematic errors usually associated with absolute measurements were minimized and did not obscure minor variations in the Z dependence of the cross sections. The measured values drop from 353 b at V to 9.9 b at Bi. The general trend of the Z dependence of the data 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.