Electron Optical and Related Design Considerations for Micro-X-Ray Sources

Abstract

The purpose of the work described in this dissertation is to investigate the design considerations associated with multipurpose micro-x-ray sources, with special emphasis on the electron optical requirements of micro sources for micro-x-ray fluorescence equipment in Forensic Science. The x-ray resolution that can be achieved by a micro-x-ray source, the appropriate x-ray target geometry, the maximum power density such an x-ray target can withstand without damage and the power dissipation in such a target are briefly discussed, Micro-radiographs obtained from an experimental single lens micro-x-ray source were used to estimate the x-ray resolution that can be achieved in practice, Experiments have also been performed to investigate the maximum power that a thin target can withstand under the heating effects of the incident electron beam, It is shown that for the electron spot sizes usually associated with Forensic micro-x-ray sources, water cooling of the target is not advantageous. Previously described electron optical columns employing conventional magnetic lenses have many disadvantages compared to those with single polepiece lenses, The optimum use of a single polepiece lens as an objective lens for the probe forming system of a micro-x-ray source has been investigated and new form of highly saturated single polepiece and asymmetric lenses have been developed, It is shown that objective lenses of this type are also well suited as objective lenses in high resolution electron microscopes intended for analytical purposes, Experimental forms of these lenses have been constructed and tested in an electron optical bench, Finally in order to test these ideas in practice, an experimental micro-x-ray source, was constructed, This was used for microradiography and for preliminary investigations in micro-x-ray fluorescence analysis.