L-Subshell X-Ray Production Cross Sections of Ba, La and Ce for Proton Energies from 0.25 to 2.00 MeV

Protons from the University of Texas at Arlington´s 2 MV Van de Graaff accelerator were used to produce characteristic L x-rays from thin targets of Ba, La and Ce. The incident proton energy was varied from 0.25 to 2.00 MeV. The x-rays were detected by a detector mounted at 90° to the incident beam direction. Measured x-ray production cross sections were converted to ionization cross sections by the use of subshell fluorescence yields and Coster-Kronig transition probabilities taken from Bambynek. Inflection points are found in the L1-subshell ionization cross section for all three elements. Although the theoretical plane-wave Born approximation (PWBA) curves do have inflection points (whereas the binary encounter approximation (BEA) curves do not), the PWBA theory does not correctly predict the proton energies at which these occur for all three elements.