Study of L-subshell ionization cross sections of Ho, Er, and Tm by α particles

The L-subshell ionization cross sections induced by 1 to 6 MeV α particles were measured for three elements of the rare earth group: holmium, erbium, and thulium. Simultaneous PIXE and RBS measurements were utilized. The measured cross sections were compared with the theoretical calculations of the ECPSSR theory. The comparison shows good agreement at high bombardment energies especially for L2 subshell. When the effect of intra-shell transitions (IS) induced by the Coulomb field of the projectile was included in the ECPSSR formalism, the systematic discrepancies between the theoretical and the experimental values at low energies were reduced. The L2 and L3 subshells discrepancies have been resolved only after the united atom effect (UA) has been incorporated into the theory. However; as the discrepancies of the L1 subshell remain to be addressed only possible reasons are discussed