Pb and BiL-subshell ionization cross-section ratios versus proton bombarding energy from 0.5 to 4 MeV

Experimental ratios of $L$-subshell cross sections are given for ionization of lead and bismuth by 0.5-4-MeV-proton bombardment. The ratio of the $L_{\mathrm{II}}$ to $L_{\mathrm{I}}$ cross sections exhibits a maximum near 1.75 MeV. Individual subshell cross sections are obtained from the experimental ratios and previous total-cross-section data. These subshell ratios and cross sections are compared with the theoretical predictions of the plane-wave Born approximation using nonrelativistic hydrogenic wave functions, of the binary-encounter approximation scaled from Mg $K$-shell cross sections, and of the binary-encounter approximation scaled from cross sections obtained using $L$-shell velocity distributions. It was found that both approximations predict the trend of the data for the $L_{\mathrm{II}}$ and $L_{\mathrm{III}}$ subshells, but that only the plane-wave Born approximation gave the proper behavior for the $L_{\mathrm{I}}$ subshell.