Spin-resolved (e, 2e) collisions

Abstract

This thesis presents the results from the triple differential cross section (TDCS) measurements, obtained from an (e,2e) experimental apparatus incorporated with a polarised electron beam source, a polarised sodium atomic beam source, and an electron polarisation polarimeter. The form at of this thesis is in six chapters. Chapter 1 gives a brief introduction to the previous work in this field of research, and the m otivation of the present work. Chapter 2 summarises the theories of electron-impact ionisation with atoms and the electron polarisation phenomena of electron-atom scattering processes. In chapter 3, a detailed description of the experimental apparatus, including the GaAs polarised electron source, the retarding-potential polarimeter, and the (e,2e) spectrometer, is presented. The investigation of spin effects in electron-xenon ionisation processes with a polarised incident electron beam is reported in chapter 4. The transversely polarised incident electron beam has a polarisation of about 24%, and the incident energy was 147 eV. Two outgoing electrons were detected in the same scattering plane of the incident electrons with the (e,2e) coincidence technique. The fast scattered electron with an energy of 100 ± 3 eV was detected at 28°, on the left side of the electron beam, and the ejected electron with an energy of 35 ±3 eV was detected at various angles on the right side of the incident beam. The TDCS for the ground state of Xe+ have been measured with an (e,2e) energy resolution which is sufficient to resolve the two fine structure levels, 5²P½ and 5²P₃/₂. Obvious spin-updown asymmetries for both 5²P½ an d 5²P₃/₂ states were observed with these kinematics. The mechanism of this polarisation phenomenon can be mainly explained by the “fine-structure effect”. Detailed experimental results, comparison with theoretical calculations, and the discussion are given in this chapter. A non-coplanar symmetric (e,2e) experiment with an excited and polarised sodium atomic beam is reported in chapter 5. In this experiment, the electron impact energy was 605 eV. The electron beam (unpolarised), sodium beam, and the laser beam intersected a t right angles in the interaction region. With right-hand circularly polarised laser-light, the sodium atom s w ere aligned and oriented to the excited state , 3p(l = 1, mi = +1). The electron momentum distribution of this state, as well as the randomly oriented ground state 3s, were probed. The experimental results, the comparison theoretical calculations, and the discussion are presented in this chapter. The recent theoretical prediction of orientational (e,2e) dichroism, as well as some experimental techniques are also discussed in this chapter as possible future perspectives. Finally a summary is presented in chapter 6. Show more