Electron capture from hydrogenic systems by positrons and positive muons.

Abstract

In the present study the cross sections of the following reactions have been calculated in the framework of the impulse approximation: e⁺ + H(1s) ---> (e⁺ e⁻)(1s) + H⁺ e⁺ + He⁺¹ (1s) ---> (e⁺e⁻)(1s) + He⁺², μ⁺ + X(1s) ---> (μ⁺e⁻)(1s) + X⁺¹ where X stands for H, He⁺¹, Li⁺², C⁺⁵, N⁺⁶, O⁺⁷ and Fe⁺²⁵. Though the impulse approximation was introduced as an improvement on the Born approximation, it was found to be systematically worse for scattering of electrons off atoms. However, for electron capture total cross sections from hydrogenic systems by positrons, in the energy range for which the impulse approximation is valid, the impulse approximation seems to be better. In this thesis the calculation shows features in the differential cross sections which indicate that even if the impulse approximation proves worse than the Born approximation for the total cross sections in these cases, the differential cross section may be better described by it.