With Eikonal Initial State Approximation For Distorted-wave Method Of Impact Ionization

Ion-atom collision ionization plays an important role in both of the fundamental physics and practical applications. In this thesis, a continuum-distorted-wave eikonal-initial-state (CDW-EIS) approximation is developed to study the collision ionization processes, especially to investigate into the ionization mechanisms. Firstly, the reaction He²⁺+ Hâ†'He²⁺+H⁺+e^- is studied, and the total cross section for the incident energies from 30 keV/u to 2 MeV/u is calculateded and compared with other theoretical and experimental results. Meanwhile, the single- and double-differential cross sections for the electron energies from 0.2 eV to 4 T (T is the kinetic energy of the electron whose velocity is equal to that of the projectile) and the ejected angle from 0° to 180° are calculated, as well as the average energy of emission electrons as a function of the projectile energy. With the help of the double differential cross section, ionization mechanisms are discussed in details. After further study of the reaction He²⁺+ Câ†'He²⁺+C⁺+e^-, it is found that electron capture to the continuum (ECC) contributes to the total cross section more than the expectation when the projectile velocity is lower than the average velocity v_e of the bound electrons. However, this result is changed when the velocity is larger than v_e. Our explanation of this phenomenon is that the contribution of ECC is effected by the "velocity matching" between the projectile and the bound electrons. To study the variation of the ionization mechanisms according to the ionization degree of the target, we calculate the process He²⁺+ C^q+â†'He²⁺+C^(q+1)++e^-(q=0-5) and, present the double differential cross sections at the ejected angle of 0° of the 1s, 2s sub-shells. In the whole calculated energy range (30 keV/u ¹0 MeV/u), the contribution of soft collision (SC) and binary encounter (BE) enhances according to the increment of the ionization degree. However, this is not the case of ECC unless the projectile energy is higher than 1MeV/u, otherwise, the ECC decreases as the ionization degree increases. This causes some interesting crossings of cross sections for the targets with different ionization degrees, which can also be explained by the idea of 'velocity matching'.