高性能CT探测器用GGAG闪烁陶瓷的能量传输机制与光产额研究

Cerium doped gadolinium gallium aluminum garnet (Ce:GGAG) ceramic scintillators are kinds of key candidate materials for CT detector. Among all the performance indicators for detectors, light yield of scintillation materials are not only related to the measurement accuracy and the spatial resolution of the detector, but also determine the X-ray dose and the injury degree of human bodies. However, the interpretation for energy transfer mechanism of ceramic scintillators, and the specific influence mechanism of its structure defects on light yield remain to be improved. Based on previous research work to stabilize the synthesis process of GGAG ceramic material, this project will deeply investigate the energy transfer characteristics under high energy radiation excitation. The influence mechanism of defects, such as oxygen vacancy and grain boundary, on the light yield will also be explored. In addition, feasible approach to control the internal defects will be proposed with the help of the first-principles calculations, and theoretical support to further improve the light yield will be provided. Moreover, this project will build a solid foundation for GGAG ceramic scitnillators to be applied in real CT detectors.

铈掺杂的钆镓铝石榴石（Ce:GGAG）闪烁陶瓷是目前CT探测器用的关键候选材料。在探测器各项性能指标中，闪烁材料的光产额不仅关系到探测器的精度与空间分辨率，而且决定着X射线剂量及其对人体的伤害程度。然而目前关于闪烁陶瓷的能量传输机制，以及结构缺陷对光产额的具体作用机理解释还有待提高。本项目基于GGAG陶瓷材料制备及工艺稳定的前期工作基础，将深入研究高能射线激发下，能量在材料内部的传输特性；探索氧空位、晶界等缺陷对光产额的影响机制；借助第一性原理计算方法，提出抑制内部缺陷的可行方案，为实现光产额的进一步提高提供理论依据；并为GGAG闪烁陶瓷实现CT探测器的实际应用打下坚实的基础。

铈掺杂的钆镓铝石榴石（Ce:GGAG）闪烁陶瓷是目前CT探测器用的关键候选材料。在探测器各项性能指标中，闪烁材料的光产额不仅关系到探测器的精度与空间分辨率，而且决定着X射线剂量及其对人体的伤害程度。如何提高材料的光输出是闪烁材料走向实际应用所需解决的关键问题。本项目采用超声辅助的化学共沉淀法合成粒径分布均匀、烧结活性高的纳米粉体，再利用离子掺杂的方法稳定GGAG陶瓷晶体结构，进而改善闪烁材料的光学性能，并大大提高其光输出。研究结果表明当Y3+离子取代Gd3+时，陶瓷透过率可达81%，绝对光输出可达61000ph/MeV，余辉为0.005%@40ms，光输出与余辉等关键闪烁性能都优于LYSO单晶与Gemstone。这为Ce:GGAG闪烁陶瓷将来在医疗CT或者其他高能射线探测领域中的实际应用打下了一定基础。.此外，本项目还通过不同掺杂材料的光谱与衰减动力学曲线分析，构建了Yb3+，Ce3+，Gd3+以及Er3+离子的能级结构与能量传递关系，计算得出Ce3+-Yb3+能量传递效率为86%。而Y3+离子的掺杂，则导致晶体场的变化，进而使得Ce3+离子的5d能级劈裂变小，这也为Y3+掺杂GGAG陶瓷光学与闪烁性能改变提供了理论解释。