基于逆泰伯-劳效应的X射线相衬成像用小型光源研究

This project is aimed to research and develop a new x-ray source of high spatial coherence and of high brightness, as the source of the inverse Talbot-Lau interferometer. By the use of the new source, the period of interference fringes at the Talbot self-image position can be enlarged to the extent that the x-ray image detector of high resolution can directly record the fringe pattern without an analyzer grating. The advantage of this new imaging system based on the inverse Talbot-Lau geometry is that the absorption, phase-contrast and dark field images can be retrieval simultaneously by only one shot. So, the development of the new x-ray source can promote the practical application of the grating-based x-ray phase-contrast imaging techniques to medical diagnosis in hospitals and to other non-destructive inspections. ..In this project we will start from the research on the principle of inverse Talbot-Lau interferometer and figure out the physical parameters of the x-ray source, by which we can perform the structure design inside the new x-ray tube according to the x-ray production mechanism of the energetic electrons impinging on the metal target. The configuration inside the x-ray tube will be optimized on the computations of electric field and the electron trajectories. At the same time, we will also analyze the diffusion properties of energetic electrons inside the diamond and tungsten by the Monte Carlo method. The process technology research of the new x-ray tube is the key tasks in this project. The diamond is selected as the substrate on which a layer of graphene is deposited following a lift-off processing to form a multiline of tungsten. The line width of tungsten is designed 1m, and the its period is 3m. After the target fabrication, it will be put into a pre-made mold and is to be embedded onto the copper anode that is also a big heat sink. A bracket will be designed and made according to the configuration of the new tube, following the cathode and the anode components to be fixed on it. Then the experimental evaluation of the new tube can be proceeded in the vacuum chamber. When completing the vacuum envelop of the cathode and anode components into a glass tube, we will evaluate the tube by pinhole imaging for focal spot test and by the inverse Talbot-Lau interferometer for phase-contrast images.

本项目研制一种新型高空间相干、高亮度X射线源，用于逆泰伯-劳效应的X射线相位衬度成像装置的光源，使泰伯距离处的干涉条纹周期增大到探测器可以直接记录的程度。其优势在于只需一个X射线相位光栅，采用单次曝光和相位恢复算法就可以同时获取物体的吸收X射线图像、相衬图像和暗场图像，促进基于光栅的X射线相衬成像技术向医学诊断等领域的实际应用发展。本项目从逆泰伯-劳成像原理出发计算给出对X射线源的物理要求，依据高能电子束轰击金属靶产生X光的原理设计X射线管结构。通过电场和电子轨迹计算，优化源的电极结构。在导热性极好的金刚石衬底上沉积石墨烯，利用剥离工艺等微制作技术完成金刚石衬底上的钨线微结构；设计阳极模具将金刚石衬底靶嵌入铜质阳极，与设计制作的阴极组件进行真空封装，形成具有微米周期性的线发射体阵列X射线源。最后从焦斑测试和成像实验两个方面对源进行评价。

本项目研制一种新X射线管，可以作为基于逆泰伯-劳效应的X射线相位衬度成像系统的光源，从而促进基于光栅的X射线相位衬度成像技术向应用领域发展。项目从两个方面展开研究，一是成像方法研究，另一个是器件工艺技术研究。前者重点研究了适合于产品化应用的单光栅相衬成像方法，包括单光栅暗场成像、图像读出新方法等。后者重点研究微米宽度线阵列焦斑X射线源，包括电子与靶作用过程的蒙特卡罗模拟、电场计算、电子轨迹计算、焦斑计算、平面阴极结构设计、结构阳极设计工艺及特性验证、X射线管封装等。最后，提出了一种与所研制的X射线管配套使用的吸收光栅的新技术，开展了原理性验证研究，从实验上验证了其可行性。本项目研究取得的成果完全符合项目申请书的预期成果，在论文、专利和人才培养方面还超额完成了申请书中列出的指标。在内容上，超额完成了全金属热复合吸收光栅的研制。项目圆满完成了计划书的全部内容，取得的成果为X射线相衬成像技术向应用发展奠定了技术和器件基础。