硅酸铋闪烁晶体的坩埚旋转下降法制备及其双读出应用研究

For the future applicaion in the International Linear Collide(ILC), Prof. Para of Fermi Lab proposed the Homogeneous HCAL (HHCAL) based on the dual-readout technique developed by Prof. Wigmans,the PI of DREAM experiment. The HHCAL will be designed to be built with only one material to detect both the scintillation and Cherenkov signals at the same time, which will reach the required high energy resolution by ILC. Due to the advantages of Bi4Si3O12 (BSO)crystal, such as high density(6.8g/cm3), low cutoff(290nm), fast decay time(100ns),green emission (490nm) radiation hard and low cost(less than half of BGO crysatls), it can act as the most suitable detecting material of dual-readout for the HHCAL, pointed out by applicant for the first time in 2008. But BSO crystal is not easy to grow especially with large section for its melt is very adhesive with complicated phase diagram and its two components (Bi2O3 and SiO2) just have nearly opposite properties. So there are always macroscopic defects such as second phase precipitations, growth spine and inclusions inside the ingots afer crystal growth. So far no perfect BSO crystals with large section have ever been achived due to these difficulties, which has been the bottleneck for BSO crystals'development and application in the near future. Here we propose a novel method to deal with BSO's crystal growth base on our advance research with modified Bridgman method. We suggest to grow BSO crysatls with the accelerated crucible rotation technique (ACRT) connecting SICCAS's modified Bridgman technique. No BSO crystals have ever been reported to be grown by this kind of Bridgman method with ACRT. ACRT will induce the forced convection in the melt during crystal growth and can control the shape of growing interface well enough to get large crystal with high qulity. The inuced forced converction will make the melt more uniform which will greatly reduce or even reomve the macroscopic defects and make it possible to achieve macroscopic defects free BSO crystals. Morever, by the rotation of crucibles, the dopants will also become more uniform to long BSO crystals which is very essential to the application in High Energy Physics. By modifying the rotation parameters, doping and component ratio, we can investige the the kinetic behaviours of crystal growth and the relationship among defects, microstructure and scintillation properties, finally get perfect and uniform BSO crystals with large section and with which to make dual-readout testing under cosmic ray, while developing the multi-crucible rotation Bridgman technique to the scintillation crystals for the HEP. Furthermore, based on the dual-readout system test bench built under the support of NFSC, the new developed BSO crystals will be adopted so as to improve the dual-readout technique for the future Homogenous HCAL experiments.

费米实验室近来提出仅用一种材料构成的均质强子量能器设想，利用双读出技术同时探测闪烁及切伦科夫辐射信号，从而得到高精度能量分辨率。 硅酸铋(Bi4Si3O12)晶体具备高密度、低吸收截止边波长、绿发光、低成本等特点，申请人08年已率先提出该晶体最适合均质强子量能器应用。但该晶体两元组分性能差异明显，相图复杂，高温熔体粘度极大，生长中易出现多相析晶、夹杂等宏观缺陷，迄今为止未见有大截面晶体生长报道，已成为实际应用的瓶颈。申请人首次提出坩埚旋转下降法的制备新思路，拟在多坩埚下降法制备基础上引入引下管（坩埚）水平旋转系统，通过旋转参数调控、组分配比优化、生长动力学、晶体缺陷与微结构、闪烁性能等研究，解决大截面硅酸铋晶体制备中的宏观缺陷及性能不均匀性难题，探索高粘度闪烁晶体的多坩埚旋转下降法制备技术方案，并利用已建双读出测试平台进行宇宙射线等双读出技术测试和研究，为实际双读出应用打下实践和理论基础。

硅酸铋(Bi4Si3O12)晶体具备高密度、低吸收截止边波长、绿发光、低成本等特点，适合均质强子量能器用探测材料应用，但其制备难题已成为该材料实际应用的瓶颈。.本项目首次提出坩埚旋转下降法的制备BSO晶体的新思路，建立了可应用于硅酸铋晶体制备的坩埚旋转下降法晶体生长装置及技术；利用该装置探索了坩埚旋转条件下硅酸铋晶体生长规律，能有效消除宏观缺陷，减少微观缺陷，获得高完整度BSO晶体；并通过生长参数、掺杂及后处理对晶体性能的影响研究，探索了高性能晶体制备及其BSO阵列的双读出测量技术及其应用，为双读出实际应用打下实践和理论基础。.本项目利用旋转下降法晶体生长技术对BSO晶体制备进行了多方面研究，不但促进了旋转下降法技术的完善，同时也增强了对BSO晶体生长规律的了解。上述本项目研究成果都可以并且已经转化应用下降法制备技术统提升，及其他氧化物晶体的高性能制备上。