透射式微焦点X射线管阳极靶的设计、制备及性能研究

The development of high-brightness, micro-focus X-ray sources has drawn a lot of attention in the field of nondestructive inspection. A microfocus X-ray (MFX) tube generates X-rays by having its anode target bombarded by high-energy electrons. But the bombardments only cover a small area whose diameter is typically on the order of micron or even less. Whereas bombardments also heat this area and the heating power is on the order of Watt, which is very large for a micron-size region. Therefore, heat generated by bombardments could elevate the temperature of that area by a large amount. So MFX tube's anode target needs to have a good heat transfer capability to avoid local overheating, which might cause partial melting in the target, or other types of failures. To achieve that, the applicants need to look into the fabrication process of the target, the target material's physical properties and how they affect the target's heat transfer capability. In the applicants' scheme, they ought to design a target with certain geometry and material composition in the first place, and to determine a method for Monte Carlo characterization of the X-ray spectra. The applicants then use resistor-network model to calculate how well the designed target could conduct heat away from the bombarded area. Guided by the computation result, the applicants will optimize their design, and then fabricate anode target using Chemical Vapor Deposition method. The target shall be tested on an MFX tube. The applicants aim not only at an anode target preliminarily qualified for MFX tube, but also at a reliable recipe to produce these targets.

高亮度微焦点X射线源的开发是近年来无损检测领域热点应用研究课题之一。由于高速电子轰击常集中于靶材上微米或亚微米级小尺度以内，靶材微区散热能力已成为限制点X射线源的强度和使用寿命的关键科学问题之一。因此，必须深入研究靶材的生长机制和相应的物理结构属性，在解决阳极靶散热及其出光性能可靠性问题的同时，实现高亮度、小焦斑X射线源。本项目依据理论分析，通过蒙特卡洛法描述X射线光谱和能量范围，利用电阻网络法建立阳极靶内部的温度场模型，采用化学气相沉积等方式生长阳极靶材及散热层薄膜，结合表征分析和出光实验测量的结果，深入研究薄膜厚度、温度及沉积方法对薄膜导热系数、出光特性的影响并探讨相应生长机制，确定透射式阳极靶的结构及实验工艺，为高亮度点X射线管的开发奠定初步理论和实验基础。

透射式微焦点X射线管具有高X射线产生效率和高辐照通量密度的特点。但由于聚焦电子束作用于透射式阳极靶，微区的能量分布、热沉积，以及产生X射线的能力均是影响X射线源的强度和使用寿命的关键。为了实现高亮度、小焦斑X射线源，我们研究了阳极靶材料的物理属性、优化阳极组件结构、阳极靶散热及其出光性能可靠性等诸多问题。本工作重要研究结果包括：（1）通过蒙特卡罗法MCNP软件描述了能量为20 keV到160 keV的电子束条件下生成X 射线的强度变化，确定金属钨薄膜透射阳极靶的最佳厚度，以及电子能量在阳极靶中的能量分布；（2）利用有限元法分析，对比了当Be和金刚石作为窗口时，大束流密度电子束轰击阳极靶时内部的温度场分布，明确了阳极靶的局域热负荷能力；（3）依据计算的结果，分别采用CVD和磁控溅射的方式，在铍、金刚石表面生长W阳极靶材；（4）解决了Be，金刚石材料与不锈钢材料的焊接问题，实现了真空密封性；（5）在自行搭建的设备和商用仪器上开展了透射式阳极靶的出光实验，考察了不同制备方法的使用性能。研究结果表明，通过蒙特卡罗法和有限元法所得出的理论预测，结合优化的制备方法所实现的透射阳极靶，可获得了良好的X射线出光效果，工作初步确定了透射式阳极靶的结构及实验工艺，为高亮度点 X 射线管的开发提供了必要的理论和实验基础。