Study of Cross Section for Ionization and Electron Capture Process

Abstract

Collision of electron and ions with atoms and molecules is common technique for extracting information from such small entities. Electron impact ionization and excitation have been actively studied by many research groups. In spite of successes of using different quantal approximations in the case of light atoms, there exist difficulty in the calculation of electron impact single and multiple ionization cross sections for heavy atoms due to mathematical complexities. The binary encounter approximation (BEA) for the investigation of single and multiple ionizations of atoms by electron and heavy charged particles impact is found to be suitable. The approximation gives reliable results consistent with the experiments. Vriens (1966) derived a more reliable classical formalism of electron impact ionization including effect of exchange and interference. Various theoretical approaches have contributed in the development of binary encounter approximation for electron-atom, ion-atom collision processes. Double ionization of atoms and ions is a four particle interaction and hence it is still impossible to carry out exact calculations for these processes. Gryzinski and Kune (1999) have derived general analytical expression for electron impact double ionization cross sections in binary encounter model to describe the direct double ionization. In the first case the two electrons may be ejected from target atom by two successive encounters of the incident particle and secondly the incident particle may knock out one target active electron and the second electron of the target is removed by first elected electron. In this work heavy charged particles impact single and double ionization cross section for Cu and Fe atoms have been calculated in binary encounter approximation using Hartree-Fock momentum distribution for the target electrons. Electron impact single ionization cross sections for Kr, Xe and single and double ionization cross sections for Fe has been carried out. Our theoretical results for electron impact single ionization of Kr, Xe and Fe using binary encounter approximation are in good agreement with the experimental data. About 94.7 % in the case of Kr, 71 % in the case of Xe, and 93.9% in the case of Fe are within ratio factor of two and hence results are in close agreement with experimental data in the given energy range. In the case of proton impact single ionization cross section of Cu about 72 % results have ratio factor less v

than 1.12 and 50% have less than 1.1. Same nature is observed in the case of Fe and about 94.7 % fall under validity region of ratio factor 2. In the case of He vi 2+ impact single ionization cross section of Cu and Fe the results agree well in intermediate and high energy region. For the He 2+ impact double ionization cross section of Cu and Fe about 75 % and 76.9 % of calculated results are in agreement with experimental results respectively. The direct double ionization of Fe is considered to be due to the ejection of loosely bound 3d and 4s electrons and also considered ionization of 3s electron to lead an excited state which results double ionization through auto ionization. Alpha particle impact double ionization of Fe and Cu have random fluctuations in the experimental observations in low energy range which are not observed in theoretical results. Further investigations are required both in experimental and theoretical methods. In different cases of single and double ionization by electron and heavy charged particles the calculated results are found to be in satisfactory agreement with the available experimental data. Theoretical knowledge of ionization cross section and collision dynamics find wide application in different fields of science. Phenomena involving electron collisions have important roles such as astrophysics, upper atmosphere of Titan, electron driven chemistry, low temperature plasma diagnostics, modeling of plasma in Tokomak, plasma processes in cometary, radiation effects, biomedical applications, display technology, astrophysics, Stellar model, radiative process in the earth’s upper atmosphere and medical application. Using a technique of Monte Carlo simulations track structure is usually used in micro and nano dosimeter to find radiation transport index in medical science. Better the results of cross sections used as simulation codes better the results of treatment in medical science. Projectile particles of ions like protons and helium deposit a large amount of their energy in a volume of a few micrometers or even nanometers and cause extensive damage to the microscopic structure of matter and results cell death in the DNA. With different suitable theoretical models one can predict reliable values of cross sections of different atoms/ions.