Investigations of physical parameters for x-ray production cross sections using EDXRF technique

Abstract

The present thesis deals with study of atomic inner-shell photoionization processes using energy dispersive X-ray fluorescence (EDXRF) technique. These processes are characterised by physical parameters, namely, the photoionization cross sections, X-ray, Auger and Coster-Kronig tansition rates, Fluorescence and Coster- Kronig yields and vacancy transfer probabilities. The independent particle models are normally used to evaluate different physical parameters. The widely used approach is based on Dirac-Hartree-Slater (DHS) model calculations in which the average potential is assumed to be same for both the initial and final states of the atom undergoing transition. The other approach is Dirac-Fock (DF) model calculations which assume different potentials for initial and final states, thereby including the exchange and overlapping effects. There is a need to provide a check on the reliability of different sets of theoretical physical parameters based on the DHS/DF models available in literature. A brief description of processes following atomic inner-shell photoionization is given in Chapter I. Subsequently, the current status of different physical parameters describing these processes has been presented in this chapter. The experimental setup used for present work and the methods of data analysis are described in Chapter II. A new energy dispersive X-ray spectrometer has been established during the course of this work. It involves sealed disc sources of 109Cd (20mCi) / 241Am (300mCi) procured from RITVERC, Russia and a Peltier cooled Si- PIN detector (AMPTEK: XR-100CR, 6mm2×500and#61549;m, FWHM 152eV at 5.9 keV, Be window 0.5 mil thick) attached to a PC based digital pulse processor (PX4, AMPTEK). The details of these radioisotopes, X-ray detector and digital pulse processor are given in this chapter. Subsequently, the basic equation describing the relation between the observed characteristic X-ray intensity with the mass of the elemental target is described.