Microfocus x-ray tube and miniaturized x-ray tube based on carbon nanotube field emitters

Abstract

X-ray tube is a device generating high energy photon by accelerating and colliding electron beam emit-ted from electron emitter to X-ray target. Since W. C. Roentgen discovered X-ray generated from discharge tube at 1895, Several type of X-ray tubes look like, thermionic emitter based X-ray tube since 1913 and carbon nanotube (CNT) field emitter based X-ray tube since 2001 have been developed to generate a higher X-ray intensity. X-ray tube has been subdivided into none-destructive inspection, clinical diagnosis, radiation ther-apy, material analysis by following its application. Microfocus X-ray tube is an X-ray generating device with micrometer size of X-ray focal spot by col-liding highly focused electron beam on X-ray target. The resolution of X-ray image can be improved by de-crease of X-ray focal spot since penumbra of x-ray object is decreasing. In this thesis part A, to develop an X-ray tube with micrometer size of X-ray focal spot, small CNT emitter that 0.5 ??m of length and 20 nm diame-ter of CNTs are chemically deposited on 0.25 mm diameter of electrochemically etched tungsten (W) tip with 5 ??m end radius has been fabricated. Electron beam is emitted from CNT emitter and accelerated without di-verse by using focusing-type triode consisted with sloped gated electrode and anode. The electron beam is further focused by a solenoidal magnetic lens to form a minimum focal spot on X-ray target. The X-ray target has been optimized to have 1.1 ??m W layer on 0.5 mm Be X-ray window as a transmission-type X-ray target. The transmission-type CNT microfocus X-ray tube has been characterized as follows; tube voltage: 40 kV, tube current: 26 ??A, X-ray target current: 23 ??A. The X-ray focal spot has been analyzed by acquisition of a magnified X-ray image of 200 meshes TEM (Transmission electron microscope) grid (Gold, thickness: 10 ??m, bar width: 35 ??m, pitch: 90 ??m). The X-ray focal spot is 4.9±0.5 ??m in vertical direction and 4.7±0.5 ??m in horizontal dir...