ELASTIC AND INELASTIC SCATTERING OF VARIOUS PROJECTILES WITH HYDROGEN AND HELIUM ATOMS

Abstract

The work reported in this thesis is author's attempt to study the elastic and inelastic scattering of various charged (e-, e+, p) and heavy particles (H, He+) with simple atomic targets• The whole work which is based on quantum mechanical approach is categorised in three parts. Under the first part a detailed theoretical study of in-elastic scattering of charged particles (r, e+, p) with helium target in ground and metastable states, is presented. The second part of the thesis contains the scattering of hydrogen atom by scattering of hydrogen and hydrogen like ions as target. In the third and last part we have studied the elastic scattering of electrons and positrons by helium and inelastic scattering of positrons by hydrogen atom. The thesis has been divided into eight chapters. In the first chapter, we give the general introduction of the subject and the basic idea of the work reported in all other chapters of the thesis. We also discuss the brief review of the previous work, theoretical and experimental developments made in the collision process during past years in connection with the present study. Various appro-ximate methods, which have been referred/used in the present work, are briefly reviewed in this chapter. In the second chapter, we study the proton-impatt excitation of helium to the n 2 sublevels. Differential and total cross-sections in the energy range (10-1000 keV) (v) are calculated using a distorted wave Born approximations.- In this approach we incorporate the distortion in both incoming and outgoing channels of the projectile of the target nucleus. To avoid the further uncertainties in the cross-sections due to input bound state wave functions, we have used accurate target wave functions of the many parameter correlated type. A good agreement is obtained with other theoretical calculations and recent experimental mea su remelts. In third chapter, we present our study of electron, positron and proton impact excitation of metastable helium (21$, 23S) to the spin allowed excited states (21/3P, 31'3p) within the framework of a consistent distorted wave Born approximation. The different excited states of helium in the calculations are represented at Hartree-Fock level. The many parameter correlated wavefunctions are also employed to examine the correlation effect on the cross-sections for such scattering process. As a test case 21S-21P transition has been considered for calculation. 'The present calcula-tions are compared with other available theoretical results and the experimental measurements. Our calculated results for differential cross-sections of 23S-23P, 33P transitions are in reasonably good agreement with the recent measure-ments. In the fourth chapter, we have reported the study of excitation of hydrogen atom and H-like ions to its discrete state (1s-2s) in collision with hydrogen atom using second Born approximation. In addition, we have also carried out the calculation using distorted-wave Born approximation to see how such calculations would reproduce the results, for both differential and total cvoss-sections, as compared with the analogous work on the electron (proton)-atom collisions. In chapter five, we have extensively studied the elastic scattering of electrons and positrons with ground (11s) and metastable (21S and 23S) states of helium atom. Model potential approach has been adopted in a consistent manner to describe the process. Present model potential consists of static (Vst), polarization (1/p01) and exchange (Vex) potentials. The Vst is obtained using accurate many parameter correlated wavefunctions. For Vp01, we have chosen various suitable forms. A semiclassical form of exchange potential (Vex) has been used in the calculation. The whole study is presented in the three different regions of incident projectiles such as low, intermediate and high energies. In chapter six we calculate the differential and total cross-sections for excitation of n = 2 sublevels of hydrogen atom by positrons. A consistent version of distorted wave approximation method,in which distortions due to static and polarization effects are incorporated in both the channels, has been used for the calculation. Coincidence parameters for 2p excited state by positrons are also reported at various positron impact energies. The results are compared with other available theoretical calculations. Chapter seven deals with the study of elastic scattering of positrons from ground (11S) state of helium. For this purpose we have used an accurate distorted wave approximation method involving the distortion of incident projectile appropriately by static, polarization •and exchange effects in the both initial and final channels. The chapter eight, summarizes the work reported in the earlier chapters and contains some comments, pointing out the drawbacksand the suggestions for their improvements.