No abstract

No abstract

No abstract

The accuracy of PIXE analysis depends on inner-shell ionization cross sections that are often calculated in the ECPSSR theory which accounts with analytical functions for the energy (E) loss and Coulomb (C) deflection of the projectile plus for the perturbed-stationary state (PSS) and relativistic (R) nature of the target's inner shell. Although the ECPSSR is within 10% overall agreement with the K-shell data -as the proton energy falls below 0.1 to 1 MeV, respectively, in ionization of light-to heavy-target atoms -the ECPSSR increasingly overestimates the empirical database of Paul and Sacher (1989). Except for an enhancement of this overestimate at low energies, a modified ECPSSR based on the Chen-Crasemann (1985, 1989) plane wave Born approximation -evaluated with the exact limits for the momentum transfers and the Dirac-Hartree-Slater wavefunctions -yields cross sections that remain within 10% of the data and the ECPSSR theory. Codes that use only the exact limits instead of the energy-loss function are confirmed to be improper for evaluation of the ECPSSR. Further enhancement of the cross sections at the low energies is limited to light target atoms after the function derived in the separated atom approach to account for the PSS effect is joined with an expression obtained in the united atom limit. An empirical database, updated with cross sections from post-1989 publications, is normalized to the modified ECPSSR theory and various forms of the Coulomb deflection factor are revisited.

Cross sections for electron capture from inner shells by fully stripped iona are calculated and compared mth data for K-shell vacancy production. A procedure for inclusion of the relativistic effect is developed, and the scheme of calculations is illustrated through sample evaluations of electron~pture crees sections.

L-shell x-ray production cross sections by 0.25 -2.5-MeV 2He ions in 28Ni, »Cu, »Ge, 33AS, 37Rb 3/Sr 3QY, 40Zr, and~Pd axe reported. The data are compared to the first-Born approximation and the ECPSSR theory that accounts for the projectile energy loss (E) and Coulomb deflection (C) as vvell as the perturbed-stationary-state (PSS) and relativistic (R) effects in the treatment of the target I.-sheH electron. Surprisingly, the first Born approximation appears to converge to the data while the ECPSSR predictions underestimate them in the low-velocity limit. This is explained as the result of improper use of single-hole fluorescence yields. A heuristic formula is proposed to account for multiple ionizations in terms of a classical probability for these phenomena and, after it is applied, the ECPSSR theory of I.-shell ionization is found to be in good agreement~ith the data.

Cross sections for electron capture from inner atomic shells by fully stripped ions, of velocities high compared to the electron velocities in the inner-shell orbits, are calculated in the second Born approximation. The theory of Drisko for electron capture by protons from hydrogen is generalized to projectiles and targets of arbitrary atomic numbers Zi and Z2, respectively. For ions of low velocity, the effects of binding and Coulomb deflection are accounted for in a manner similar to that of Brandt and his co-workers in the theory for direct ionization to the continuum of the target atom. The results are in good agreement with experimental capture cross sections, whereas the Oppenheimer-Brinkman-Kramers approximation overestimates such cross sections.The contribution of electron capture to inner-shell ionization cross sections increases with increasing Z, /Z, and brings them into agreement with experiment.

No abstract