Joint Cryogenic Radon Emanation Measurement Facility

当今物理学中最大的两个挑战是理解暗物质的本质和中微子的特性。尽管暗物质据信占宇宙质量的85%，但它从未被直接观察到，所以我们不知道它是什么。虽然我们知道中微子有质量，但我们不知道具体有多少，也不知道它们是否是自己的反粒子。如果是这样的话，就可以解释宇宙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地影响我们对宇宙及其演化的理解。旨在探测与星系暗物质粒子相互作用的实验，或观察将告诉我们中微子的无中微子双β衰变特征的实验，都有一个共同的要求：这两个过程都极为罕见，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、矿井或山脚下，以限制来自太空的宇宙射线轰击地球表面的速度。在此之后，探测器被铜、铅和水等被动材料屏蔽，以阻挡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——探测器本身必须由不含微量放射性同位素污染的纯净和异常清洁的材料制成。英国在罕见事件地下物理方面拥有国际知名的专业知识，这是几十年来建立起来的，今天我们继续在最敏感的实验中发挥重要作用。我们拥有先进的技术来筛选材料中固定的放射性污染物，这是迄今为止主要背景的传统来源，以限制其影响并实现前所未有的实验灵敏度。我们可能即将发现下一代暗物质和中微子实验。然而，为了满足这些未来仪器的科学范围，我们必须处理新出现的背景，这些背景不能用常规方法筛选，也不能通过分析技术轻易拒绝。这个背景是稀有气体，氡。氡是作为材料中微量铀和钍的衰变产物在材料中产生的，但与其他子代不同，它可以扩散并填充整个目标体积。为了应对未来实验的这一关键挑战，我们必须开展研发和高度敏感的氡辐射测量，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，我们必须在不同温度下对大量材料进行分析，因为氡辐射取决于材料类型、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，没有一个能满足未来大样本实验和模拟大多数实验条件的要求。根据这项提议，我们将在卢瑟福阿普尔顿实验室提供一个独特的氡辐射测量设施，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双β衰变社区。无论为这些探测器选择何种技术，该系统都将为即时研发和未来实验提供全新的能力，因为所有探测器都需要解决氡问题。这样的设施将对各种各样的应用非常有用，远远超出了物理学。它将改进用于医疗和核监测部门进行低辐射测量的商用设备，并改进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，因为氡在导致肺癌方面的突出作用仅次于吸烟。

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.