Excitation of SnK- andL- and TaL-shell x rays by 1.4-4.4-MeV protons

Excitation functions and absolute cross sections for Sn $K$- and $L$-shell and Ta $L$-shell x-ray production by proton impact have been measured over the energy range 1.4-4.4 MeV with a Si(Li) detector. The results, combined with our measurements on other elements, are compared with existing theories. In the calculation of ionization cross sections from the plane-wave Born approximation, we discuss the effect of a relativistic correction for the ionization potential. The plane-wave Born approximation with the correction due to the Coulomb deflection gives the best fit for Sn $K$ x-ray production and the binary-encounter approximation is the best for Sn $L$ and Ta $L$ x-ray production. The semiclassical approximation based on the impact-parameter treatment predicts values which are not in agreement with the data on Sn $L$ x rays. The scaled universal excitation curve based on the binary-encounter approximation gives good fits to $K$-shell ionizations but seems to show some disagreement for $L$-shell ionizations. The dependence of the $\frac{K\alpha }{K\beta }$ ratio of Sn on the target thickness was investigated but it was found that the ratio is constant within the experimental uncertainty. Relative intensities for the transitions $L\alpha$, $L\beta$, $L\gamma$, and $L_l$ are also compared with the theories.