RII Track-4: Research and Development of Ring-Contact Germanium Detectors

如果中微子被证明是它们自己的反粒子，它可以解释宇宙中物质比反物质更普遍的原因。唯一在实验上可行的回答这个问题的方法是寻找无中微子双贝塔(0νββ)衰变，这是一种提出的核衰变形式。较大的Ge晶体具有较高的体积表面积比，这有利于在寻找0νββ衰变的过程中收集信号和抑制背景。格尔达和马约拉纳的演示已经证明，可以在足够低的本底下建立一个基于Ge的吨级实验，以获得能够潜在发现0νββ衰变的灵敏度。这项RII Track-4计划将开发大尺寸Ge环接触(GERC)探测器，以进一步降低背景、复杂性和成本。这项拟议的研究将推动GE探测器技术在宇宙学、天文学、国土安全和工业应用中的应用。该项目的成果将发表在学术期刊上，并通过与工业界的合作进行传播。研究活动与教育和推广工作紧密结合：研究生和本科生都将参与该项目，从而获得Ge晶体提纯和探测器开发方面的尖端技能和专业知识。本科生教育和外展活动的主要重点是鼓励妇女攻读STEM专业。无中微子双β(0νββ)衰变的大型浓缩Ge实验的灵敏度目标(LENGE-1000)要求本底水平为≤1×10^(-5)事件/kev/kg/年。Legend-1000更喜欢大尺寸探测器(每个探测器3公斤)，这将进一步降低背景、复杂性和成本。这项RII Track-4计划将通过研发(R&D)使用南达科他州大学生长的高纯度Ge晶体的GERC探测器来探索大尺寸探测器。在德克萨斯农工大学(TAMU)的拉斯蒂·哈里斯教授(东道主)和北卡罗来纳大学教堂山分校(UNC)的约翰·威尔克森教授(合作者)的合作下，PI将在TAMU制造GERC探测器，并在北卡罗来纳大学进行测试。目前，联想-200已经成功地测试了倒置同轴点接触(ICPC)Ge探测器，其典型质量为~2公斤。为了进一步增加每个探测器的质量，基于GERC探测器的新的探测器概念是很有前途的，因为它可能被用来制造大到~6公斤的Ge探测器。尽管它们已经被建模，但GERC探测器还没有被制造出来，并对其能量分辨率和脉冲形状属性进行测试。由于大尺寸Ge晶体中的电荷收集不完整，Ge探测器的能量分辨率下降，这也将是Legend-1000的一个障碍。该项目将帮助解决三个关键挑战：制造质量约2-3公斤的GERC探测器，测量大尺寸GERC探测器的能量分辨率和脉冲形状辨别，以及分析美元生长的晶体的质量。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

If neutrinos are proven to be their own anti-particles, it can offer an explanation of the prevalence of matter over anti-matter in the universe. The only experimentally feasible way to answer this question is to look for neutrinoless double-beta (0νββ) decay, a proposed form of nuclear decay. Large Ge crystals have a higher volume-to-surface ratio which is advantageous for the collection of signals and rejection of backgrounds in a search for 0νββ decay. GERDA and MAJORANA DEMONSTRATOR have proved that a Ge-based ton-scale experiment can be built with sufficient low-background that will achieve a sensitivity capable of the potential discovery of 0νββ decay. This RII Track-4 proposal will develop large-size Ge ring-contact (GeRC) detectors to further reduce backgrounds, complexity, and cost. The proposed research will advance Ge detector technology for cosmology, astronomy, homeland security, and industrial applications. Results from this project will be published in scholarly journals and disseminated through collaboration with industry. Research activities are closely integrated with education and outreach efforts: both graduate and undergraduate students will work on the project, thus gaining cutting-edge skills and expertise in Ge crystal purification and detector development. The main focus of undergraduate education and outreach activities is to encourage women to pursue STEM majors. The sensitivity goal for the Large Enriched Ge Experiment for Neutrinoless double beta (0νββ) Decay (LEGEND-1000) requires a background level of ≤1×10^(-5) events/keV/kg/year. LEGEND-1000 prefers large-size detectors (3 kg per detector), which will further reduce backgrounds, complexity, and cost. This RII Track-4 proposal will explore large-size detectors through research and development (R&D) on GeRC detectors using high-purity Ge crystals grown by the University of South Dakota (USD). With the collaboration of Professor Rusty Harris (Host) of Texas A&M University (TAMU) and Professor John Wilkerson (collaborator) of University of North Carolina at Chapel Hill (UNC), the PI will fabricate GeRC detectors at TAMU and test them at UNC. Currently, LEGEND-200 has successfully tested inverted coaxial point-contact (ICPC) Ge detectors that have a typical mass of ~2 kg. To further increase the mass per detector, a new detector concept based on GeRC detectors is promising, as it can potentially be used to make a Ge detector as large as ~6 kg. Although they have been modeled, a GeRC detector has yet to be fabricated and tested for its energy resolution and pulse shape properties. The degradation of energy resolution seen with Ge detectors that is due to incomplete charge collection in large-size Ge crystals will also be an obstacle for LEGEND-1000. This project will help to resolve three key challenges: fabrication of a GeRC detector with a mass of ~2 – 3 kg, measurement of the energy resolution and pulse shape discrimination in a large-size GeRC detector, and analysis of the quality of USD-grown crystals.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.