K-Ionization Cross Sections for Relativistic Electrons

Experimental values of the $K$-shell ionization cross section are determined from scintillation spectrometer measurements of the $K$ x rays emitted when thin targets of tin and gold are bombarded by 50-, 100-, 200-, and 500-keV electrons. For these energies and atomic numbers, the experimental results show differences from the cross sections given by Burhop's nonrelativistic calculations and by Perlman's relativistic calculations, but show good agreement with the predictions of Arthurs and Moiseiwitsch, who employed relativistic free-particle wave functions for the projectile electron and nonrelativistic wave functions for the atomic electron.