Liquid Xenon Purification for Dark Matter Detection

该提案要求普林斯顿大学的一个小组为暗物质探测器开发一种液态氙净化技术。现在从天体物理学的测量中可以确定，宇宙中大约30%的物质是由某种新形式的“暗物质”组成的。这种暗物质不同于构成我们所熟悉的日常物质的原子，之所以如此命名，是因为它不发光，也不以普通的方式与物质相互作用。相反，暗物质存在的证据来自于这种物质在广泛的天体物理系统中产生的引力，从小的星系到宇宙中已知的最大的星系群。在不确定暗物质是什么的情况下，人们认为暗物质可能偶尔会与普通物质的原子发生碰撞。因为我们的星系也充满了暗物质，一个足够灵敏的粒子探测器，类似于盖革计数器，可以在地球上看到这些粒子的碰撞。然而，为了有机会探测到这些幽灵般的粒子，必须大大降低天然放射性背景的普通水平。一些小组正在开发基于惰性气体氙的液化形式的探测器。液态氙将作为被暗物质粒子撞击的目标。氙自然地以低水平存在于空气中，当从空气中商业分离出来时，它含有一定量的氪，另一种惰性气体。一个问题是，氪含有微量的放射性同位素，虽然对人体健康可以忽略不计，但对氙基暗物质实验来说却是一个严重的问题。PI建议开发一种新方法，将氪从Xe中去除到这些实验所需的水平。

This proposal requests support for a Princeton group to develop a liquid xenon purification technique for a Dark Matter detector. It now appears certain from astrophysical measurements that some 30% of the total amount of material in the universe is composed of some new form of "dark matter". This dark matter is distinct from the atoms that make up the everyday matter we are familiar with, and is so named because it does not emit light, or interact with matter in an ordinary way. Instead, the evidence for dark matter comes from the gravitational attraction this matter exerts in a wide range of astrophysics systems, from galaxies at the small end, to the largest groupings of galaxies known in the universe. Without knowing with certainty what this matter is, it is thought likely that dark matter may occasionally collide with the atoms of ordinary matter. Because our galaxy is also full of dark matter, a sensitive enough particle detector, analogous to a Geiger counter, could see collisions of these particles here on Earth. However, ordinary levels of natural radioactive backgrounds must be reduced enormously for this idea to have a chance of detecting these ghostly particles. A number of groups are developing detectors based on a liquefied form of the inert gas xenon. The liquid xenon will serves as the target to be struck by the dark matter particle. Xenon naturally occurs in air at a low level, and, when separated from air commercially, contains some amount of krypton, another inert gas. A problem is that krypton contains trace amounts of a radioactive isotope, which, while negligible for human health, is a serious problem for xenon-based dark matter experiments. The PI proposes to develop a new method to remove Kr from Xe to the level needed for these experiments.