Theoretical Study On Angular Properties Of Auger Electrons Of Nonradiative Decay Following Electron-Impact Excitation Of Berylliumlike Ions

Electron-impact excitation of atoms or ions is one of fundamental atomic processes in astrophysical and laboratory plasmas.The Auger electrons emitted from the nonradiative decay following the electron-impact excitation of atoms or ions are always spin polarized and anisotropic.When compared with Auger decay rates and Auger energies,spin polarization and angular distribution of Auger electrons can provide more detailed information on the excitation and subsequent nonradiative decay of ions.Furthermore,as one of the dominant relativistic effect,the effect of the Breit interaction on angular distribution of Auger electrons was never studied.In this thesis,angular properties of Auger electrons for nonradiative decay following electron-impact excitation of highly charged berylliumlike ions are studied within the framework of the density matrix theory of atomic transitions,the relativistic multiconfigurational Dirac-Fock method,and the fully relativistic distorted-wave theory.The main contents are given as follows:1.Based on the work of Chen and Reed,the electron-impact excitation from the ground state to the autoionizing level 1s2s²2p_1/2J=1 and the subsequent nonradiative Auger decay 1s2s²2p_1/2J=1→1s²2s J=1/2 of berylliumlike Mg⁸⁺,Fe²²⁺,Mo³⁸⁺,Nd⁵⁶⁺,Au⁷⁵⁺,and U⁸⁸⁺ions is studied.Special attention has been paid to the effect of the Breit interaction on the angular distribution of the Auger electrons emitted.It is found that for low-Z ions the Breit interaction hardly contributes to the angular distribution,while for medium-and high-Z ions the Breit interaction contributes to lowering the anisotropy of the angular distribution,which first becomes quickly more prominent with increasing atomic number up to certain high-Z ions and then behaves very slowly less prominently for higher-Z ions.In particular,at the impact energy of 3.0 times the excitation thresholds,the effect of the Breit interaction on the angular distribution of the Auger electrons for high-Z ions is found to be nearly independent of the atomic number Z,which is quite different from the situation for the angular distribution of the characteristic x-photons radiated from the identical autoionizing level following the identical electron-impact excitation process of berylliumlike ions.2.On the basis of the above work,to explain the difference between the effects of the Breit interaction on the angular distributions of both the Auger electrons and the characteristic photons,the effect of the Breit interaction on electron-impact excitation from the ground state to the 1s2s²2p_1/2J=1 autoionizing level and the subsequent nonradiative Auger decay 1s2s²2p_1/2J=1→1s²2s J=1/2 of berylliumlike Nd⁵⁶⁺,Ho⁶³⁺,Re⁷¹⁺,Pb⁷⁸⁺,Ra⁸⁴⁺,and U⁸⁸⁺ions is studied.It is found that for high-Z beryllium ions the contribution of Breit interaction to the excitation amplitude makes the alignment parameters is close to 0 at the impact electron energy of three times their respective excitation thresholds,which result in the angular distribution of Auger electrons is almost isotropic and the relative contribution of Breit interaction to the anisotropy parameters is almost independent on the atomic number Z.Moreover,due to the competition between the effects of the Breit interaction on both of the alignment parameters and the intrinsic anisotropy parameters,the relative contribution of the Breit interaction to the anisotropy parameters is smaller than the relative contribution to the intrinsic anisotropy parameters at the impact electron energies of 2.0,3.0,and 4.0 times excitation thresholds respectively.In particular,the effect of the Breit interaction on the angular distribution of Auger electrons for high-Z berylliumlike ions decreases with increasing atomic number due to the change of sign of the anisotropy parameters at the4.0 times excitation threshold.