RUI: Radioactive Krypton Background Evaluation by Atom Counting

这项建议涉及开发一种新技术，该技术基于用于稀有Kr同位素放射性测年的原子陷阱痕量分析(ATTA)方法，以测量低至3x10^(-14)水平的其他稀有气体的Kr含量。基于液体稀有气体的新一代探测器为令人兴奋的新发现提供了一条很有希望的途径。这些探测器包括氙暗物质搜索项目，以及XMASS和清洁中微子探测项目，所有这些项目都依赖于使用液体氙气或霓虹灯作为闪烁介质来探测低能量下的罕见事件。在所有这些系统中，氪-85的β衰变是背景事件的一个重要且有问题的来源。85Kr在化学上是惰性的，半衰期为10.76年，这使得它极难与其他稀有气体分离。氙气探测器需要的Kr/Xe丰度最多为10^10，而XMASS和CLEAN探测器需要的Kr/Xe或Kr/Ne最多为10^14的1。用传统的商业技术无法保证这种纯度水平。在ATTA方法中，要分析的气体样本被引入到一个设备中，该设备使用激光冷却技术来冷却和捕获原子束中处于亚稳态的Kr原子。用灵敏的光电探测器探测被捕获原子的激光荧光，直接测量陷阱负载率，可以高信噪比地计数单个被捕获的原子。Kr丰度可以通过比较超纯样品和已知Kr含量的样品的载荷率来确定。更广泛的影响拟议的测量将有助于表征这些新探测器的本底水平，从而有助于氙气、清洁和XMASS的工作。此外，ATTA技术可能对研究级气体制造商具有一定的商业价值。这项技术可以扩展到检测Kr以外的元素，并测量远低于传统技术可能水平的杂质气体。这可能使制造比目前可能的纯度更高的气体成为可能，这将对许多领域的研究人员有用。

This proposal addresses the development of a new technique, based on the Atom Trap Trace Analysis (ATTA) method used for radioactive dating with rare Kr isotopes, to measure the Kr content of other rare gases at levels as low as 3x10^(-14). A new generation of detectors based on liquid rare gases offers a promising avenue for exciting new discoveries. These detectors include the XENON dark matter search project, and the XMASS and CLEAN neutrino detection projects, all of which rely on the use of liquid xenon or neon as a scintillation medium to detect infrequent events at low energies. In all of these systems, the beta decay of krypton-85 is a significant and problematic source of background events. 85Kr is chemically inert, and has a half-life of 10.76 years, making it extremely difficult to separate from other rare gases. The XENON detector will require Kr/Xe abundances of at most one part in 10^10, and the XMASS and CLEAN detectors will require Kr/Xe or Kr/Ne of at most one part in 10^14. This level of purity cannot be guaranteed with conventional commercial techniques. In the ATTA method, a sample of the gas to be analyzed is introduced to an apparatus that uses laser cooling techniques to cool and trap Kr atoms in a metastable state from an atomic beam. Single trapped atoms can be counted with high signal-to-noise by detecting the laser fluorescence of the trapped atoms with a sensitive photodetector, directly measuring the trap loading rate. The Kr abundance can be determined by comparing the loading rate for an ultra-pure sample to that of a sample with known Kr content. Broader ImpactThe proposed measurements will aid in the XENON, CLEAN and XMASS efforts by helping characterize the background levels in these new detectors. Additionally, the ATTA technique may be of some commercial interest to manufacturers of research grade gases. The technique can be extended to detect elements other than Kr, and to measure impurity gases at levels well below those possible with conventional techniques. This may enable the manufacture of gases of higher purity than is currently possible, which would be useful to researchers in many fields.