低温晶体量热器用低本底钼酸锂晶体制备及其应用研究

For the future dark matter and neutrino exploration, neutrinoless double beta decay is proposed as the most effective method based on cryogenic crystal bolometer which is featured as high energy resolution and low background. .The CUORE has achieved very interesting results, which uses TeO2 as the detective crystals. And CUORE is planning the upgrade with patricle identification as CUPID with more effective crystal candidate. Lithium molybdate（Li2MoO4，LMO）crystal has better properties than the in-use TeO2 and act as the most suitable detecting material. But LMO crystal is not easy to grow for it's a bi-component of Li2O and Mo3, which make it more difficult to get high purity crystals than TeO2. And there are always macroscopic defects such as second phase precipitations, growth spine and inclusions inside the ingots afer crystal growth. So far no high purity and low background LMO crystals with large section have ever been achieved due to these difficulties, which has been the bottleneck for LMO crystals'development and application in the near future..Here we propose a novel method to deal with LMO's crystal growth base on our advance research with modified Bridgman method. We suggest to grow LMO crysatls with the accelerated crucible rotation technique (ACRT) connecting SICCAS's modified Bridgman technique. No LMO 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 as well as dopants and make it possible to achieve macroscopic defects free and high purity LMO crystals. Moreover, by the rotation of crucibles, the dopants will also become much less which is very essential to the application in cryogenic crystal bolometer. By modifying the rotation parameters and component ratio, we can investigate the the kinetic behaviors of crystal growth and the relationship among defects, microstructure and scintillation properties, finally get perfect and uniform LMO 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 low temperature system test bench built under the support of NFSC, the new developed LMO crystals will be adopted so as to improve the technique for the future dark matter experiments.

无中微子双贝塔衰变(0vββ)实验不但能探测中微子质量的绝对值，而且是检测中微子是否为Majorana粒子的唯一途径，现已成为国际上粒子及核物理领域研究的科学前沿。在新一代的0vββ实验规划中，低温晶体量热器探测路线具有极高能量分辨率、低本底、较低成本等优势，是具有极强竞争力的技术选择。钼酸锂（Li2MoO4，LMO）晶体以其优越的性能，已超过氧化碲等成为量热器探测材料的首选。本项目瞄准低温量热器用高纯低本底钼酸锂晶体，借鉴研制高纯氧化碲晶体的成功经验，探索固相法及液相法（含重结晶法）合成高纯多晶料，利用坩埚旋转下降法创新思路生长大尺寸高纯低本底钼酸锂晶体；同时探索钼酸锂晶体在低温环境中的光-热双读出行为以及量热器探测应用，反馈改进多晶料制备工艺及坩埚旋转下降法晶体生长技术，最终得到能应用于量热器的大尺寸低本底钼酸锂晶体，为推进国内低温晶体量热器技术及应用打下坚实的实验及理论基础。

钼酸锂（Li2MoO4，LMO）晶体已成为低温晶体量热器的核心探测材料。本项目已成功地研发出大尺寸高纯钼酸锂晶体制备技术，有望推进该晶体在用于CUPID及CUPID-CJPL实验中的实际应用。.本项目成功利用氢化工艺提纯了市售碳酸锂原料，利用升华法提纯了市售氧化钼原料；在此基础上，提出了水溶液法合成钼酸锂多晶料的新思路，可以得到比传统固相合成法更高纯度的多晶料。本项目建立了下降法生长钼酸锂晶体的制备技术，同时提出了两次生长技术思路，即首先使用提拉法进行第一次快速生长，目的注重排杂效应，然后应用下降法进行第二次生长，目的注重晶体生长的完整性，同时兼顾排杂效应。该两次生长工艺能有效地进一步提高了晶体的纯度，同时利用退火工艺保证了晶体的完整性。本项目为国内外唯一掌握下降法制备大尺寸高纯钼酸锂晶体的制备技术。此外，本项目还探索了钼酸锂晶体的掺杂行为，有望拓宽该晶体的应用领域。.本项目为富100Mo的大尺寸低本底钼酸锂晶体的制备及其应用打下了坚实的实验及理论基础。