Theoretical And Experimental Study Of X-ray Source With Micro-beam

The x-ray source with micro-beam is an x-ray source with 1.0~100um x-ray spot's diameter and with high enough brightness. The source is very important in such scientific researches and applications as biomedicine, biochemical dynamics, industrial nondestructive examination and detection, x-ray microscopy and micro-CT.Several different types of x-ray source with micro-beam are currently being used, such as conventional x-ray tubes and other electron-beam devices, synchrotron radiation source, laser plasmas bombing target, being cooperated with one or two x-ray optical elements as Bragg-Fresnel zone plates, multilayer mirrors into the x-ray regime, or x-ray lens. Most of these x-ray sources are large, complex, and expensive.The x-ray source with micro-beam that we developed avoids several fundamental limitations in comparison with traditional ones. The novel x-ray source is based on the fact that when the high energy electron-beams with micro-focus bombard metal target, it would radiate x-rays with micro-beam. The source has two fundamental parts, electron-emitting system and focusing system. The former consists of LaBe crystal cathode, Wehnelt grid and an accelerating anode, and the latter is comprised of two equal radius concentrating cylinder electrodes.It's well known that the x-ray radiation emitted by electron-beams acting on metal target surface has well developed for about 100 years. So, our main work is to obtain a satisfactory electron beam with diameter about micrometers by means of choosing a suitable LaBe cathode electron-gun system and a suitable focusing system.In theory, firstly, the numerical simulation methods, such as the boundary element method (BEM), the finite difference method (FDM) and the finite element method(FEM), were utilized to calculate the distribution of electric field intensity and potential of the electron-gun system, the focusing system and the whole equipment, respectively. Then, the trajectories of the electron-beam were traced by using of the Runge-Kutta method and the Monte-Carlo method associatively. The point spread function (PSF) was also calculated. Finally, It is according to the size of the whole instrument and the PSF that we chose the optimal electrodes' parameters, e.g. configuration and position and potential. The results show that when the temperature of LaB6 cathode is about 1900-2000K and it emits current saturation 58.3-141.4uA, the full width of half maximum (FWHM) of electron-beam spot focused onto the surface of metal target is only l.Oum or so.In the subsequent experiments, when the LaBe cathode emitted continuously and the current is 40uA, the minimum diameter of electron-beam spot recorded was 22 um. While the LaB6 emitted pulse, the minimum diameter of the focus decreased and wasn't more than 15um. The reason is that the heat accumulated on the foil-film, which enlarged the focus dimension, reduced remarkably.The x-ray source with micro-beam we developed, not only can be located inindividual research laboratories and used by researchers because it's a convenient and simple source which is so small and so low-cost, but also can be facilely and safely moved and manipulated. Furthermore, the source can be used to ameliorate and enhance the spacial resolution of existing medical transmission imaging and x-ray micro-CT images. It is well-founded believed that our x-ray source with micro-beam will help the advance in the studies of biology, medicine, life sciences, and material science, etc.