Electron-impact ionization for Kr atom

Electron-impact ionization cross sections for the ground level of the Kr atom are studied using the scaled distorted-wave (DW) approximation. It is demonstrated that the DW cross sections calculated in the potential of the ionizing ion overestimate the experimental data at low and medium energies of the impacting electron. The scaled DW results, that include in calculations the value of the ionization threshold provided by National Institute of Standards and Technology, lead to good agreement with the measurements. A negligible contribution from the indirect process of the ionization to the total ionization cross sections is obtained in the final results. The study demonstrates that the higher ionization stages appear as a result of the ejection of additional electrons from the atomic system by the sequential ionization.