Relativistic wave-function effect on theK-shell ionization of Sb, Gd, Yb, Au, and Bi by low- to intermediate-velocity F ions

Abstract

We have measured absolute cross sections for the K-shell ionization of medium- and high-Z targets of Sb, Gd, Yb, Au, and Bi induced by low- to intermediate-velocity F ions having energies between 2.5 and 5.8 MeV/u. Our main interest is to see the effect of the relativistic nature of the K-shell electrons of these target atoms on the ionization cross sections. The information on the degree of relativistic effect has been obtained by comparing the measured data with different theoretical calculations with and without including the relativistic corrections. A comparative study of the two different models such as SCA (semiclassical approximation) and ECPSSR [perturbed stationary state (PSS) including the corrections for energy (E) loss, Coulomb (C) deflection, and relativistic (R) effects] is presented. It is shown that the SCA calculations with the relativistic wave function predict an ionization cross section that is at least an order of magnitude higher compared to that given by the nonrelativistic calculation for Bi target. This factor is reduced to about 2 in the case of Sb. The ECPSSR, however, predicts lower ratios for the relativistic to nonrelativistic calculations. The experimental results, in general, are in good agreement with the SCA calculations using relativistic wave functions as well as with the ECPSSR model. For high-Z targets the SCA gives slightly better agreement with the data compared to the ECPSSR. In addition, it is shown that in the ECPSSR formalism the ionization cross sections of high-Z (with large relativistic effect) as well as low-Z targets (with less relativistic effect) can be scaled approximately to follow a universal curve after including the relativistic correction.