氟化钡晶体闪烁光慢成分的选择性掺杂抑制

Presently, barium fluoride (BaF2) crystal is fastest inorganic scintillator known, but its slow scintillation component can cause serious problems with pileup at rates above a few hundred kHz. Barium fluoride with slow component effectively suppressed is very promising for the future fast electromagnetic calorimetercalorimeters at the intensity frontiers for particle physics and may also find widely applications, such as fast and time of flight imaging. Selective doping has been investigated as an efficient avenue to suppress the slow scintillation component for barium fluoride crystals and has received much attentions in the past research. In this proposal, three doping ions (La3+, Y3+ and Lu3+), which have been proved to be efficient in suppressing the slow component of BaF2 crystals, will be revisited and their characteristics and mechanism of slow component suppression will be further investigated. Alkali metal ions, such as Li+, Na+ and K+, etc., will be tentatively introduced into BaF2 as dopants or co-dopants, and their characteristics and mechanism of possible slow component suppression will be thoroughly examined. The preparation and scintillation properties of large sizes lanthanum doped barium fluoride crystals will be systematically investigated to evaluate their potentiality for fast calorimeters at the intensity frontiers. We will examine the distribution characteristics of La3+, Y3+ and Lu3+ in BaF2 crystals and investigate their influence on the scintillation performance of doped BaF2 crystals. The crystal growth, La3+ distribution, and scintillation performance of BaF2:La3+ crystals and alkali metal ions co-doped BaF2:La3+ crystals will be comparatively studied with an emphasis on understanding the impact of alkali metal ions as co-dopants. Through the study of this proposal, it is expected that the suppression mechanisms of BaF2 crystal by selective doping could be further understood and the timing characteristics could be improved.

氟化钡（BaF2）是目前已知最快无机闪烁体，但在计数率超过几百kHz测量时，其闪烁光慢成分会引起严重的信号堆积。如果其慢成分能被有效抑制，该晶体有望用于未来粒子强度前沿装置的电磁量能器及其它高速和飞行时间技术成像领域。选择性掺杂作为一种抑制氟化钡晶体慢闪烁成分的有效途径，受到了广泛关注。本项目拟从已证实较为有效的三种离子La3+、Y3+和Lu3+的出发，进一步研究这些离子的慢分量抑制特性和机理；并尝试将碱金属离子以单掺或共掺的形式引入BaF2，详细地探讨这些离子可能的慢分量抑制特性和机制；开展大尺寸La3+掺杂BaF2晶体制备及其闪烁性能的系统性研究，并评估其用于强度前沿快电磁量能器的可能性。研究La3+、Y3+和Lu3+在BaF2晶体中的分凝特性及其对掺杂BaF2晶体闪烁性能的影响，探讨碱金属离子共掺对BaF2:La3+晶体生长、La3+离子分凝和闪烁性能等的影响。

氟化钡（BaF2）晶体是一种具有亚纳秒发光的无机闪烁体，但其慢分量会在高计数率时引起严重的信号堆积，抑制了其在超快辐射探测领域（高能物理实验、GHz硬X射线成像和飞行时间技术正电子湮没断层扫描）的应用。但BaF2晶体还有一个峰值位于300nm，衰减时间约600ns，发光强度5倍于快发光分量的慢发光分量，该慢分量会在高计数率应用时造成严重的堆积效应，限制了其广泛应用。抑制BaF2晶体的慢分量对其在超快领域的应用至关重要。选择性掺杂作为一种抑制其慢闪烁成分的有效途径，受到了研究领域的广泛关注。本项目以三种掺杂离子（La3+, Ce3+和 Y3+）抑制超快闪烁体氟化钡（BaF2）晶体的发光慢分量为研究对象，较为系统地研究了La3+、La3+/Ce3+和Y3+离子掺杂BaF2晶体的晶体生长、透光性、发光性、快/慢分量比、衰减动力学和抗辐照损伤等闪烁特性，分析了La3+、La3+/Ce3+和Y3+离子掺杂对快/慢发光分量的影响，详细探讨了它们抑制慢分量的物理机制。光学和闪烁特性表征研究表明，5at%Y掺杂可以在不影响快分量的情况下，将BaF2晶体的慢分量降低至纯1/10，Y掺杂在抑制BaF2晶体的慢分量具有很好的潜力。通过制备工艺条件的探索和优化，制备出长度达200mm长的大尺寸、高质量La、La/Ce和Y掺杂BaF2晶体。对它们包括发光性能和光响应均匀性等性能的闪烁特性特性进行了系统地研究，对这些大尺寸掺杂BaF2晶体用于强度前沿快电磁量能器的可能性进行了评估；研究La3+、Ce3+和Y3+在BaF2晶体中分布规律和分凝特性，评价了掺杂离子的分布特性对BaF2晶体光学透过和光响应均匀性的影响。本研究为该稀土离子掺杂BaF2晶体在未来高能物理强度和能量前沿实验的电磁量能器、超快硬X射线自由电子激光及飞行时间技术成像领域的应用奠定了较好的研究基础。