Collaborative Research: ARI-MA: Realizing high performance inorganic scintillators at low cost

合作研究：ARI-MA：以低成本实现高性能无机闪烁体

• 批准号: 1348361
• 负责人: Richard Williams
• 金额: $ 12.96万
• 依托单位: Wake Forest University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-10-01 至 2015-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1348361&HistoricalAwards=false
• 关键词: Collaborative; Research; ARI; MA; Realizing

1348361 (Williams), 1348139 (Burger), and 1348341 (Biswas). The Global Nuclear Detection Architecture (GNDA) is intended to detect illicit and unregulated nuclear and radiological materials worldwide. Wide deployment calls for quick and accurate detection technology with sensitivity and resolution close to current state-of-the-art scintillators but at much lower cost. The basic premise of this approach is that there are already inorganic scintillators with light yield and proportionality close to the limits that can be achieved in their ~5 eV band gap range; and that this group haswe developed a predictive model that describes why there is a sweet spot of material parameters defining the current group of highest performance scintillators. This is used to narrow the scope of theoretical, crystal-growth, and evaluative searches in this project so that they can be targeted farther into ternary and quaternary compositions and at the same time deeper into parameters that affect cost and performance. Some of the best new scintillator hosts are in fact composed of abundant (cheap) elements. The reason for their current high cost is not materials, but low yield of growing large single crystals. This project will pursue four research avenues to solve or side-step the crystal growth problems on the way to realizing an economical detector from materials in the sweet spot of structures, compositions, and physical parameters identified from the design rules developed by Wake Forest, Fisk, LBNL, and others since about 2010. One of the approaches to reduce cost examines how to improve the proportionality of segmented index-matched assemblies of smaller crystal blocks that are difficult to grow in large sizes. Such segmented detectors combined with wavelength shifting also provide flexibility to deal with self-absorption (photon diffusion) that currently limits the size of SrI2:Eu detectors. The group will measure and model how the peripheries of blocks in segmented scintillators contribute to nonproportionality, and what can be done to improve it. One ultra-lowcost but high-risk possibility involves index-matched granular scintillators using pre-doped SrI2:Eu beads supplied in bulk by chemical manufacturers. Starting with an excellent scintillator like SrI2:Eu, guided by experience with the segmented scintillators and their modeling, and applying thermal and chemical processing to the beaded material, the group will investigate the physics of what limits the resolution of granular detectors and how to advance performance beyond prior index-matched granular scintillators. A third approach to cost reduction will raise the yield of crystal growth by hardening and toughening existing excellent scintillators while taking care that the hardening measures do not degrade proportionality and light yield. A fourth targets theoretical and experimental searches toward new ternary and quaternary crystals with cubic structures and other properties favoring large crystal growth as well as slow electron thermalization, poor hot electron mobility, good thermalized electron mobility, and low Auger rates leading to best proportionality and light yield. Three university teams bring to this quest their complementary expertise and facilities in (1) crystal growth and characterization, (2) ultrafast laser probes of scintillation and associated numerical modeling of transport, trapping, and nonlinear quenching, and (3) electronic structure calculations on candidate crystals, defects, and dopants. The intellectual merit lies in applying this complementary three university array of experimental and theoretical techniques guided by predictive physical models to attack the cost problem treated in terms of physical parameters alongside those determining proportionality and light yield in both gamma and neutron detectors. The results, positive or negative, will inform the whole field on the models and methods employed. The broader impacts will be to increase national and global security by making possible improved, affordable deployment of nuclear monitoring; increasing the pool of U.S. university graduates trained in the materials technologies necessary to build and deploy such systems widely; and instituting a 3- university bridge system of interacting undergraduate, M.S., and Ph.D. programs and opportunities among the participating universities in three southeastern states to provide a path into the nuclear detection workforce for under-represented and economically disadvantaged students.

1348361(威廉姆斯)、1348139(汉堡)和1348341(比斯瓦斯)。全球核探测架构旨在探测世界各地非法和不受管制的核材料和放射性材料。广泛的部署要求快速准确的检测技术，其灵敏度和分辨率接近当前最先进的闪烁体，但成本要低得多。这种方法的基本前提是，已经有无机闪烁体的光产额和比例接近其~5 eV带隙范围内可以达到的极限；并且这一组闪烁体已经开发出一个预测模型，该模型描述了为什么存在定义当前最高性能闪烁体组的材料参数的甜蜜点。这是用来缩小该项目的理论、晶体生长和评估研究的范围，以便它们可以更进一步地针对三元和四元组分，同时更深入地研究影响成本和性能的参数。一些最好的新闪烁体主持人实际上是由丰富(廉价)元素组成的。它们目前成本高的原因不是材料，而是生长大单晶的成品率低。这个项目将通过四个研究途径来解决或绕过晶体生长问题，在实现经济探测器的过程中，从结构、成分和物理参数的甜蜜点材料，根据维克森林公司、FISK、LBNL和其他公司自2010年以来制定的设计规则确定。降低成本的方法之一是研究如何提高难以在大尺寸中生长的较小晶体块的分段折射率匹配组件的比例。这种与波长移动相结合的分段式探测器还提供了处理自吸收(光子扩散)的灵活性，这种自吸收目前限制了SrI2：Eu探测器的尺寸。该小组将测量和模拟分段闪烁体中块的外围是如何造成不成比例的，以及可以做些什么来改善它。一种超低成本但高风险的可能性涉及使用化学制造商批量供应的预掺杂SrI2：Eu微珠的折射率匹配颗粒闪烁体。从像SrI2：Eu这样的优秀闪烁体开始，以分段闪烁体及其建模的经验为指导，并对珠状材料进行热处理和化学处理，该小组将研究限制颗粒探测器分辨率的物理因素，以及如何超越以前折射率匹配的颗粒闪烁体的性能。第三种降低成本的方法将通过硬化和增韧现有的优秀闪烁体来提高晶体生长的产量，同时注意硬化措施不会降低比例性和光产额。第四个目标是从理论和实验上寻找具有立方结构和其他性质的新的三元和四元晶体，这些晶体具有大的晶体生长以及缓慢的电子热化、较差的热电子迁移率、良好的热化电子迁移率和低的俄歇速率，从而获得最佳的比例性和光产额。三个大学团队为这一探索带来了他们在以下方面的互补专业知识和设施：(1)晶体生长和表征，(2)闪烁的超快激光探测器和相关的输运、陷阱和非线性猝灭的数值模拟，以及(3)关于候选晶体、缺陷和掺杂的电子结构计算。智力上的优点在于，在预测物理模型的指导下，应用这三所大学互补的实验和理论技术阵列，以解决根据物理参数处理的成本问题，以及决定伽马和中子探测器的比例和光产额的成本问题。无论是积极的还是消极的结果，都将向整个领域通报所采用的模型和方法。更广泛的影响将是，通过使改进的、负担得起的核监测部署成为可能，加强国家和全球安全；增加受过材料技术培训的美国大学毕业生队伍，这些材料技术是建立和广泛部署此类系统所必需的；建立一个由三所大学组成的桥梁系统，在东南部三个州的参与大学之间开展本科生、硕士和博士项目，并提供机会，为代表性不足和经济困难的学生提供进入核检测队伍的途径。