LYSO闪烁晶体的能量分辨率研究

As a promissing scintillation material for the next generation Calorimetry in High Energy Physics (HEP) and Time-of-Flight PET (TOF-PET) machine, LYSO crystal has attracted much attention because of its high Light Output (L.O.), high density,fast decay, good timing resolution and excellent radiation harness. The L.O. of LYSO crystal is reported to be 4 to 5 times as that of BGO crystal, its Energy Resolution (E.R.), however, found to be at the same level as BGO crystal. In other words, the E.R. in LYSO is relatively low in viewpoint of its L.O. The moderate E.R. of LYSO crystal will affect the performance of Calorimetry and the PET machine resulting in a relatively poor E.R.of Calorimetry and imaging quality of PET machine. While most research works on LYSO crystal nowdays focusing on the crystal growth and the improvement of light output, no study was found dedicated to improve the E.R.in LYSO crystal.This work will focus on the study of energy resolution in LYSO crystal by studying systematically the infuence of crystal quality such as optical transmission, the density of luminescent center,the uniformity of crystal, the state of defects and its density on the E.R. in LYSO crystal. By doing so, we will try to figure out the corresponding correlation between the E.R. and parameters mentioned above. This work will then study the interaction between the crystal qualities and the scintillation mechanism in LYSO crystal to unveil the very reason why the E.R. in LYSO is not as good as expected. All these efforts will enrich the knowledge of scintillation materals and help to develop high quality LYSO scintillation crystal for future HEP experiments and Medical Imaging.

LYSO是综合性能优良的闪烁晶体。具有高光输出、高密度、快衰减、很好的时间分辨率和辐照硬度；是目前闪烁材料研究的热点材料，也是新一代TOF－PET和下一代高能物理实验高亮度量能器的首选闪烁材料之一。虽然LYSO的光输出是BGO的4－5倍，但目前LYSO的能量分辨率却与BGO相当，远未达到与其光输出相应的水平；相对较差的能量分辨率限制了用LYSO作探头的PET机成像质量和量能器性能的进一步提高。目前，对LYSO的研究主要集中在晶体生长和光输出的提高上，已有的报导均未对其能量分辨率的提高作系统的研究。本研究拟系统地从晶体光学质量、发光中心浓度、晶体均匀性、缺陷及其浓度等方面入手，查明影响LYSO晶体能量分辨率提高的主要因素；结合闪烁机理研究，阐明影响LYSO晶体能量分辨率提高的本质原因，为开发更高能量分辨率的LYSO晶体奠定研究基础。

摘要.通过本项目实施，获得了优化的晶体生长温场，有效克服了晶体开裂并生长了直径80mm等径长度180mm的大尺寸LYSO晶体；本研究查明了LYSO晶体中最优铈离子浓度：研究表明铈离子在150—400ppmw的范围内，LYSO光输出有一个相对稳定的‘平台’，在此范围内LYSO的光输出基本不受铈离子浓度的改变的影响。这一结果对于研发高能物理用大尺寸LYSO晶体、提高成像用LYSO的成品率具有重要的指导意义。利用单光子计数TSL技术对LYSO的相关缺陷进行了研究，发现余辉对应360K TSL，该缺陷的能级约0.95eV。高掺杂（铈浓度大于400ppmw）的LYSO在580K处出现一个新TSL峰，对应能级为1.31eV缺陷；此缺陷的形成有可能是造成高掺LYSO晶体能量分辨率恶化的原因。大尺寸LYSO晶体生长面上铈离子的离散性较小，本研究测得籽晶端和尾端铈离子的离散性分别为6.3%和3.9%；对于一致性有较高要求的核医学应用等领域，应尽量生长大直径、较短的晶体。研究阐明，铈离子浓度的不均匀性是导致能量分辨率恶化的重要因素。.本项目发表SCI论文5篇，申请中国发明7项，有7篇报告为本专业国际会议接收。