科研之友
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摘要
When the continuum distorted wave with eikonal initial state (CDW-EIS) [D. S. Crothers and J. F. McCann, J. Phys B 16, 3229 (1983)] theory is applied to the evaluation of ionization cross sections, many additional approximations are assumed. However, usually, the influence of these approximations is not clear. Aiming to estimate them, we compare the differential and total cross sections obtained with diverse approximations for ionization of He atoms by proton impact. We analyze the post-prior discrepancy, which depends on the perturbative Hamiltonian applied in the scattering amplitude. We study the dependence of the cross sections on the description of the initial and final states. For this purpose, we use the 1Z and 5Z variational and numerical Optimized Potential Model (OPM) [J. D. Talman, Comput. Phys. Commun. 54, 85 (1989)] bound states for the initial target state, and for the final target state we set Coulomb waves with proper effective charges or the continuum state of an OPM potential model. The cross sections resulting from OPM post and prior versions are identical and show excellent agreement with experimental data in each case. Nevertheless, the cross section derived by the prior CDW-EIS, 5Z initial wave, and corresponding continuum state gives comparable results, requiring shorter computational work. Then we study the determination of the impact parameter ionization probability from the transition amplitudes, also including an axial symmetry for the ionization process. The hypothesis of this axial symmetry saves an angular integration in the evaluation of the probabilities. We analyze the variation of these probabilities within the post and prior formalisms and mention initial and final states, according to the supposed symmetry. We found that the probabilities derived with the axial symmetry concentrate at a lower impact parameter than the usual ones and are quite sensitive to the approximations used for the CDW-EIS evaluation. Furthermore, these probabilities underestimate distant collisions. In the last section we introduce the projectile-residual ion potential, and we discuss the effect of the diverse approximations on the dependence of the cross section as a function of the projectile scattering angle. We compare the projectile angular distribution resulting from a full Coulomb interaction between the ions with the one obtained by a screened potential, but in the latter case the theoretical distributions underestimate the experimental data. The OPM and 5Z functions give a good description of the experimental data.
- 出版日期2011-3-25
