根据端窗透射Micro-CT靶材的理论模型设计了W-Al透射靶材的基本结构, 结合Geant4计算模拟软件和Müller的靶温升计算模型分别确定了W靶面和Al基体的厚度. 以YXLON光机的W-Al透射靶材结构参数为依据, 采用磁控溅射法在Al基体表面分别制备了厚度为2, 5和8 μm的W薄膜, 并借助SEM进行微观形貌分析, 得到了致密度和均匀度均较好的W薄膜靶面. 借助YXLON的X射线管, 对3种不同厚度靶材的X射线出射率及其对应所需功率进行了实验研究, 结果表明: W靶面的最佳厚度是5 μm, 此时, 靶材的X射线出射率最大且产生X射线所需的功率最小. 在此基础上, 进行了X射线出射率和X射线成像效果的对比实验, 结果表明: 无论在X射线出射率及其所需功率方面, 还是在X射线成像效果方面, W靶面厚度为5 μm的W-Al透射靶材的性能均优于YXLON W-Al透射靶材, 能够满足Micro-CT所需的高质量靶材的应用要求.

Micro-computed tomography is a new three-dimension high-resolution imaging device, which due to its X-ray brightness generated by a compact electron impact X-ray source. To achieve higher X-ray brightness, the size of the X-ray source should be as small as possible. However, the X-ray brightness is fundamentally limited by the maximum possible heat dissipation of the X-ray target. As an electron beam strikes a metallic target, the power density of target is increased with the decreasing of the spot size of electron beam, which results in the decrease of the X-ray brightness by significant temperature elevation of the target surface. A practical solution for these requirements is the use of a multi-film target consisting of a thin-film target on a thicker substrate film. The substrate should be composed of a light material with high thermal conductivity to prevent absorption of the signal X-rays and to elevate the target temperature. In such a multi-film target, several factors as following must be considered to choose the materials and thicknesses of the multiple films: the highest power density of the target can sustain without performance degradations or damage, and the efficiency of the X-ray generation in the target material including any self absorption effects. The present work designed a basic structure of tungsten-aluminum transmission target, according to the theoretical model of the end-window transmission target for Micro-CT. The thicknesses of tungsten target surface and aluminum substrate are determined by the Geant4 simulation results and the Müller calculation model of temperature rise, respectively. According to the structure parameter of tungsten-aluminum transmission target of YXLON, the tungsten film with the thickness of 2, 5 and 8 μm are prepared on the aluminum substrate by the magnetron sputtering method. The density and evenness of tungsten film both are well by the SEM analysis. The performance of three kinds of target with different thicknesses is carried out on the X-ray tube of YXLON. The results show that the optimal thickness of tungsten film is 5 μm, and the X-ray emitting efficiency of tungsten-aluminum transmission target is the biggest, which the corresponding production power of X-ray is the lowest. On this basis, the contrast experiments of X-ray emitting efficiency and X-ray imaging effect are carried out between the tungsten-aluminum transmission target of homemade and that of YXLON. The experimental results indicate that the X-ray emitting efficiency, the corresponding X-ray production power and the X-ray imaging effect of homemade target all are superior to that of YXLON, which could be satisfied the application requirements of high quality target for Micro-CT.