$M$-subshell ionization cross sections of Au, Pb, Bi, and U by proton bombardment were obtained over the projectile range 0.3-4.0 MeV. X rays were detected by Si(Li) spectroscopy. At least one characteristic radiative transition line for each $M$ subshell was isolated and measured. Radiative and nonradiative branching ratios were taken from theoretical calculations of Bhalla and McGuire. Our total x-ray-production cross sections are compared with the measurements of other authors. Comparison of our scaled subshell ionization cross sections with calculations in the plane-wave Born approximation shows, in general, good agreement. Uncertainties in fluorescence yields and in super—Coster-Kronig coefficients can introduce great imprecision in some experimentally determined subshell ionization cross sections.

• Received 18 October 1982

DOI:https://doi.org/10.1103/PhysRevA.28.2770