L-shell ionisation of medium and heavy elements by 1.2-3.0 MeV incident alpha particles

Abstract

Thin targets of Yb, W, Au, Pb and Bi were bombarded by 1.2-3.0 MeV alpha particles. From the resulting L X-rays experimental Li-subshell ionisation cross section were deduced. The measured cross sections are compared with the predictions of the ECPSSR theory by expressing the data in terms of ratios of experimental to theoretical values as a function of the corrected reduced velocity xi (Li)R. Disagreements of up to 50% were revealed for the L1 subshell at xi (L1)R<or=0.3. The ECPSSR theory underestimate the L2 ionisation cross sections for all elements studied by as much as a factor of 3.3 but explains the L3 data to within 30%. In general, for heavy elements, the ECPSSR is unsuccessful in explaining the velocity dependence of the cross sections. Several factors were highlighted which may explain some of the observed disagreements. The target atomic number dependence of the experimental Li subshell and total ionisation cross sections were also investigated and the results are presented.