Applications of the impulse approximation to atomic collision processes

Abstract

The first and major part of this thesis deals with electron capture collisions, while the second part is concerned with excitation of atomic hydrogen by electron and proton impact. In Chapter 1 the formal theory of scattering is used to obtain an exact expression for the cross section for electron capture by a structure-less particle in atomic hydrogen, and the Born series of approximations is introduced via a formal expansion of the Green's operator for the system. Chapter 2 begins with a discussion of the OBK approximation; relevant experimental investigations are then briefly described, a number of Born approximation calculations are discussed and a detailed description is given of some impact parameter methods which have proved useful in this field. The chapter ends with remarks on some very recent work. The impulse approximation is derived in Chanter 3 and the evaluation of cross sections for the processes and is described in detail. Results for these processes are presented and are compared with the values obtained by other authors. The behaviour of electron capture cross sections in the high energy limit forms the subject of Chapter. Most of the standard approximations are discussed but the main emphasis is placed on the Born and impulse approximations, for which the analysis is given in detail. The application of the impulse approximation to the excitation of atomic hydrogen by electron and proton impact is discussed in Chapter 5. It is shown that the results obtained by Akerib and Borowitz for electron impact are unreliable. New results are given which are in poor agreement with experiment and reasons for the discrepancy are discussed.