Sample preparation equipment for ultra low background screening with ICP-MS

“暗物质”--一种将星系凝聚在一起的神秘物质，占宇宙质量的85%，令人难以置信。许多人认为它是由弱相互作用的大质量粒子(WIMP)组成的--但它们还没有被实验检测到。这是因为它们很少从原子上反弹，而且很弱，因此它们的存在极难被检测到。尽管如此，科学家们一直致力于构建能够记录WIMP相互作用的灵敏探测器。问题是，在这些探测器中还有许多其他粒子相互作用，这可能会掩盖少数微弱的WIMP。由于WIMP相互作用如此罕见，因此实验必须屏蔽从太空轰炸地球的所有宇宙射线，迫使它们深入地下。然而，这仍然不足以提供所需的安静环境；因此，它们不会受到地下岩石中发现的自然放射性的影响--对我们无害，但对敏感设备来说是灾难性的。最后一个背景仍然存在，它来自制造探测器的材料。微量的铀和钍通过放射性衰变产生信号，这些信号通常与WIMP的预期信号难以区分。这意味着必须进行广泛的材料筛选活动，以便在构建探测器时只选择最纯净的材料。为了寻找WIMP，开发更灵敏的探测器要求越来越清洁的建筑材料。然而，我们现在已经达到了技术成熟，我们的下一个探测器可以具有理论上预测的最终探测暗物质的灵敏度。问题是，用来建造它们的材料的筛选能力没有跟上步伐。我们传统上依靠“高纯锗”探测器(HPGe)来测量材料，然后再用它们来建立实验。然而，HPGe需要数周时间才能筛选出一个样本--在未来几年里，我们需要检查数百种材料，这是不可接受的。此外，HPGe实际上不能直接测量U和Th。相反，它测量U和Th衰变成的元素。电感耦合等离子体质谱(ICPMS)能够直接测量U和Th。它不能像HPGe那样告诉我们U和Th的衰变产物，但它们一起产生了我们需要的完整图像。此外，筛选材料所需的时间--大约一天或更短时间--正是建立下一代实验所需要的。然而，ICPMS要求所有的材料都要准备好--溶解在酸中，然后以液体的形式引入。ICPMS只有在材料消化、制备和引入干净的情况下才能达到高灵敏度。在传统技术下，开放式玻璃器皿中的加热材料暴露在元素中，灵敏度可能会显著下降。这项建议是为了加强英国现有的ICPMS，使用封闭式微波灰化和具有超纯、高浓度、侵蚀性酸的消化烤箱，以支持英国的暗物质研发计划。这样的新能力将在几个小时内提供令人难以置信的灵敏度。这将把英国的研发项目提升到独特的世界级地位，无论是现在还是将来，此时国际上的HPGe和ICPMS设施都难以满足需求，也不具备足够的灵敏度。它还将有助于其他需要超低活动的罕见事件搜索，例如那些寻求观察无中微子双β衰变的搜索。这些实验可以告诉我们中微子的基本性质，并以此解释大爆炸后不久粒子和反粒子之间的微小不平衡，这是今天任何物质存在所必需的。ICPMS还在食品安全、制药、环境、法医和临床研究中有强大的应用，在这些研究中，低水平污染物的元素分析是一个具有重大社会和经济影响潜力的丰富研究领域。

'Dark Matter' - a mysterious substance that holds the galaxies together makes up an incredible 85% of the mass of the Universe. It is believed by many to be made up of Weakly Interacting Massive Particles (WIMPs) - but they have not yet been detected experimentally. This is because they bounce off atoms only very rarely and weakly such that their presence is extremely difficult to detect. Despite this, scientists have been working on constructing sensitive detectors capable of registering WIMP interactions should they occur. The trouble is that there are many other particles interacting in these detectors that may mask the few and faint WIMPs.Since WIMPs will interact so rarely the experiments must be shielded from all the cosmic-rays bombarding Earth from space, forcing them deep underground. However, this is still not enough to provide the quiet environment required; they are therefore shielded from natural radioactivity found in underground rock - harmless to us but catastrophic to the sensitive devices. A final background remains, coming from the very materials the detectors are made from. Tiny amounts of uranium and thorium produce signals by radioactive decay that are often indistinguishable from those expected from WIMPs. This means that extensive material screening campaigns must be conducted to select only the purest materials in constructing detectors.Developing ever more sensitive detectors in the hunt for WIMPs has demanded ever-cleaner construction materials. However, we have now reached a technological maturity such that our next detectors could have the sensitivity theoretically predicted to finally detect Dark Matter. The trouble is that capability to screen materials from which to construct them has not kept pace. We have traditionally relied on 'High Purity Germanium' detectors (HPGe) to measure materials before using them to build experiments. However, HPGe requires many weeks to screen a single sample - unacceptable when we need to check hundreds of materials in the coming years. Furthermore, HPGe cannot actually measure U and Th directly. Instead it measures elements that U and Th decay into.Inductively Coupled Plasma Mass Spectrometry (ICPMS) is capable of measuring U and Th directly. It cannot tell us about the decay products from U and Th as HPGe can, but together they produce the complete picture we need. Moreover, the time taken to screen materials - about a day or less, is just what is called for in building the next generation of experiment. However, ICPMS requires all materials to be 'prepared' - dissolved in acid and introduced as a liquid. ICPMS will only achieve high sensitivity if the materials are digested, prepared and introduced cleanly. With traditional techniques, heating materials in open glassware exposed to the elements, sensitivity can suffer dramatically.This proposal is to enhance the UK's existing ICPMS with closed microwave ashing and digestion ovens with ultra-pure, high concentration, aggressive acids, to support the UK's Dark Matter R&D programme. Such new capability would give incredible sensitivity, in only hours. This would elevate the UK's R&D programme to unique world-class status now and well into the future, at a time when internationally HPGe and ICPMS facilities are struggling to cope with demand and do not possess enough sensitivity.It will also aid other rare event searches that require ultra-low activity, such as those seeking to observe neutrino-less double beta decay. These experiments could tell us about the fundamental properties of neutrinos, and in doing so explain the tiny imbalance between particles and anti-particles shortly after the Big Bang needed for any matter to exist today. ICPMS also has powerful application in food safety, pharmaceutical, environmental, forensic and clinical studies, where elemental analysis of low levels of contaminants is a rich area of research with significant societal and economic impact potential.