Development of High-Purity NaI(T1) Crystals for the SABRE Dark Matter Experiment

天体物理学观测和宇宙学数据提供了强有力的证据，表明近四分之一的宇宙由暗物质组成。弱相互作用大质量粒子（wimp）和轴子在理论上被认为是暗物质的首选候选者。尽管有强有力的证据证明暗物质的存在，但wimp和轴子都没有被最终探测到。DAMA/LIBRA实验声称十多年来已经用一系列低本底NaI（Tl）晶体闪烁体探测到了暗物质。然而，使用不同探测器进行的其他实验并没有发现暗物质存在的证据，尽管它们具有很高的灵敏度。由于对暗物质的灵敏度可能取决于探测器材料的细节，因此需要使用比DAMA/LIBRA低得多的背景NaI（Tl）探测器来寻找暗物质的证据。该奖项将资助SABRE（主动背景抑制的碘化钠）实验，该实验的重点是开发比DAMA/LIBRA更低背景的新晶体。高纯度晶体的发展可以影响许多研究领域，甚至可能影响目前有微量放射性影响其可靠性的半导体。这项工作还涉及许多领域，吸引了背景广泛的学生。SABRE还促进与工业合作伙伴的牢固关系，然后为所有客户带来新的产品和服务。与RMD， Sigma Aldrich， Seastar Chemicals和Sandfire的合作为市场带来了高纯度的产品和敏感的分析服务。与梅伦公司的合作导致了一项发明，可用于净化材料的效率更高。由该奖项资助的研究将支持开发和测试低背景NaI（Tl）晶体探测器，该探测器利用普林斯顿大学与梅伦公司合作开发的新的区域精炼技术，以改善目前用NaI-33建立的记录；以及在西班牙坎弗朗实验室开发地下晶体生长设施。SABRE将分为两个阶段：第一阶段包括在意大利格兰萨索实验室（Gran Sasso Laboratory， LNGS）安装一个探测器，作为测试晶体放射性纯度的原理验证（PoP）；在第二阶段，将在北半球和南半球建造双探测器。SABRE-south计划安装在SUPL （Stawell地下物理实验室）中，这是澳大利亚正在建设的一个新的地下实验室。这两个探测器将提高将暗物质信号与季节性和局部效应区分开来的可能性。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Astrophysical observations and cosmological data give strong evidence that nearly a quarter of the Universe consists of dark matter. Weakly interacting massive particles (WIMPs) and axions have been proposed as theoretically favored candidates for dark matter. Despite the strong evidence for the existence of dark matter, neither WIMPs nor axions have been conclusively detected. The DAMA/LIBRA experiment claims for more than a decade to have detected dark matter with an array of low background NaI(Tl) crystal scintillators. However, other experiments with different detectors have not seen evidence for dark matter, even though they have very high sensitivity. Because the sensitivity to dark matter may depend on details of the detector material, a new search for evidence of dark matter with NaI(Tl) detectors with much lower background than DAMA/LIBRA achieved is needed. This award will fund the SABRE (Sodium-iodide with Active Background REjection) experiment which has been focused on the development of new crystals with lower background than DAMA/LIBRA. The development of high purity crystals can affect many fields of research, perhaps even semiconductors which presently have trace levels of radioactivity that affect their reliability. The effort also involves many fields and attracts students with a wide range of backgrounds. SABRE also promotes strong relationships with industrial partners, who then brought new products and services to all customers. Collaboration with RMD, Sigma Aldrich, Seastar Chemicals, and Sandfire has brought high purity products and sensitive assay services to the market. Collaboration with the Mellen Company has led to an invention that can be used to purify materials with higher efficiency.The research funded by this award will support the development and testing of a low-background NaI(Tl) crystal detector exploiting the new zone-refining technique developed by Princeton in collaboration with Mellen Company in order to improve the present record established with NaI-33; and the development of a crystal growth facility underground at the Canfranc Laboratory, Spain. SABRE will have two phases: phase 1 consists of one detector at the Gran Sasso Laboratory (LNGS), in Italy, which works as a proof-of-principle (PoP) for testing the radio-purity of crystals; in phase 2, twin detectors will be built in the northern and southern hemispheres. The SABRE-south is planned to be installed in the SUPL (Stawell Underground Physics Laboratory), a new underground laboratory in Australia under construction. The two detectors will enhance the potentiality to differentiate a dark matter signal from seasonal and local effects.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.