Joint Cryogenic Radon Emanation Measurement Facility

当今物理学面临的两个最大挑战是理解暗物质的性质和中微子的性质。尽管暗物质被认为占宇宙质量的85%，但它从未被直接观测到，所以我们不知道它是什么。尽管我们知道中微子有质量，但我们不知道它们到底有多大，或者它们是否是自己的反粒子。如果是这样的话，这可以解释大爆炸后不久物质和反物质之间的微小不平衡。这些问题的答案将深刻影响我们对宇宙及其演化的理解。旨在探测与银河系暗物质粒子相互作用或观察无中微子双β衰变特征的实验有一个共同的要求：这两个过程都极其罕见，因此探测器必须屏蔽所有为微弱信号提供背景的辐射源。第一道防线是将探测器放置在地下深处的实验室、矿山或山下，以限制来自太空的宇宙射线轰炸地球表面的速度。在此之后，探测器被铜、铅和水等被动材料屏蔽，以阻止来自地下实验室环境的辐射，特别是来自岩石的辐射。最后一步是最困难的--探测器本身必须由纯净的材料建造，没有放射性同位素的微量污染。英国在稀有事件地下物理方面拥有国际知名的专业知识，几十年来积累起来的，今天我们仍然在最敏感的实验中发挥着重要作用。我们拥有先进的技术来筛选固定在材料中的放射性污染物，这是迄今为止主要背景的传统来源，以限制它们的影响并实现前所未有的实验灵敏度。随着下一代暗物质和中微子实验的到来，我们可能即将发现。然而，为了满足这些未来仪器的科学影响，我们必须解决一个新出现的背景，这个背景不能用常规方法筛选，也不能通过分析技术轻易拒绝。这个背景是惰性气体--氡。氡是作为材料中痕量铀和钍的衰变产物在材料中产生的，但与其他子体不同，它可以扩散并填充整个目标体积。为了解决未来实验的这一关键挑战，我们必须进行研发和高灵敏度的氡发射测量，作为我们分析活动的一部分，以选择合适的建筑材料，并建立表征氡传输和预期背景的模型。此外，我们必须在不同的温度下分析大量的材料，因为氡的释放取决于材料的类型、暴露的表面积和材料的温度。在世界上为数不多的高灵敏度氡系统中，没有一个系统满足未来大样本实验的要求，也没有一个系统能在模拟大多数实验的条件下进行实验。有了这项提议，我们将在卢瑟福·阿普尔顿实验室提供一个独特的氡发射测量设施，以支持英国的罕见事件搜索研究，特别是暗物质和无中微子的双贝塔衰变社区。该系统将为立即的研发和未来的实验提供全新的能力，无论这些探测器选择的技术是什么，因为所有这些探测器都需要处理氡。这样的设施将对远远超出物理学的各种应用有用。它将允许改进用于医疗和核监测部门进行低辐射测量的商业设备，并增强用于测量家庭和工作场所氡水平的低成本氡探测器，以确保安全水平，因为它在导致肺癌方面发挥着重要作用，仅次于吸烟。

Two of the biggest challenges in physics today are to understand the nature of dark matter and the properties of the neutrino. Although dark matter is believed to make up an incredible 85% of the mass of the Universe, it has never been directly observed and so we do not know what it is. And though we do know neutrinos have mass, we do not know precisely how much or if they are their own anti-particles. If they are it could explain the tiny imbalance between matter and antimatter shortly after the Big Bang. Answers to these questions will profoundly impact our understanding of the Universe and its evolution. Experiments that aim to detect interactions with galactic dark matter particles or observe the signature of neutrino-less double beta decay that will tell us about the neutrino share a common requirement: both processes are extremely rare and so detectors must be shielded from all sources of radiation that present background to the faint signals. The first line of defence is to place the detectors in deep underground laboratories, in mines or under mountains, to limit the rate of cosmic rays from space that bombard the Earth's surface. After this the detectors are shielded with passive materials like copper, lead and water to block radiation from the underground laboratory environment, particularly from the rock. The last step is the most difficult - the detectors themselves must be constructed from pure and exceptionally clean materials that are free from trace contaminations of radioactive isotopes.The UK has internationally renowned expertise in rare-event underground physics, built up over several decades, and today we continue to hold major roles in the most sensitive experiments. We have advanced techniques to screen materials for radio-contaminants fixed within them, the traditional source of major backgrounds to-date, to limit their effect and achieve unprecedented experimental sensitivities. We may be on the edge of discovery with the next generation of dark matter and neutrino experiments. However, to meet the science reach of these future instruments, we must address an emerging background that cannot be screened with regular methods, nor easily rejected through analysis techniques. This background is the noble gas, radon. Radon is produced in materials as a decay product of trace uranium and thorium in materials, but unlike other progeny, it can diffuse out and populate entire target volumes.To address this key challenge for future experiments we must perform R&D and highly sensitive radon emanation measurements as part of our assay campaigns to select suitable construction materials and to build models that characterize radon transport and expected backgrounds. Moreover, we must assay large amounts of materials and at different temperatures, since radon emanation is dependent on material type, exposed surface areas and on the temperature of the material. Of the few high sensitivity radon systems around the world, none meet requirements for future experiments for large samples and in conditions that mimic most experiments. With this proposal we will deliver a unique radon emanation measurement facility to be located at the Rutherford Appleton Laboratory to support the UK's rare-event search research, particularly the dark matter and neutrino-less double beta decay communities. The system will enable entirely new capability for immediate R&D and for future experiments, regardless of the technology chosen for these detectors since all will need to address radon.Such a facility would be useful to a wide variety of applications well beyond physics. It would allow improvements in commercial devices that are used to perform low-radiation measurements for the medical and nuclear monitoring sections, as well as enhancing low-cost radon detectors that are used to measure radon levels in homes and the workplace to ensure safe levels given its prominent role in causing lung cancer, second only to smoking.