Investigation of Neutron-Induced Backgrounds on 134.136Xe for Large-Scale Neutrinoless Double-Beta Decay Experiments

原子核的放射性衰变过程已经为人所知有一段时间了。通常的衰变过程被称为β衰变，即原子核释放出一个高能电子，从而将中子变成质子，同时释放出一种被称为反中微子的幽灵粒子。对这一过程进行了测量并建立了理论模型，结果非常一致。在极少数情况下，一些原子核可以同时发射两个电子和两个反中微子，这一过程被称为双衰变。这个过程很难测量，因为它非常罕见，也很难计算，因为核结构的不确定性。本研究的目的是通过测量与双β衰变过程相关的核反应来减少核结构的不确定性。这将有助于理解无中微子双β衰变的实验，这是一种未观察到中微子的β衰变过程。对这种难以捉摸的衰变模式的探索已经被核科学咨询委员会确定为核科学面临的最重要的问题之一，因为这些实验将提供有关中微子和反中微子基本特性的关键信息。双重衰变实验的一个潜在背景贡献来自中子撞击源材料或附近的屏蔽材料。这些中子可以产生更多的中子，或者可以产生伽马射线来模拟所需的信号。目前有几个实验正在研究同位素氙-136的无中微子双β衰变。一种类似的同位素氙-134也以杂质的形式存在，最近发现当氙-134被中子撞击时会发出潜在的背景事件。该奖项的研究将使用高度富集的气态氙靶来调查这一最近发现的背景。气态氙样品将在三角大学核实验室用中子照射，然后将在低背景计数设施中使用屏蔽的高纯度锗探测器进行计数。在该奖项下进行的研究将扩展我们对氙潜在双β衰变背景的了解，这将有助于规划未来的吨级中微子双β衰变实验。由于观测中微子双β衰变是核科学长期计划的主要组成部分，因此获得有关背景的信息是必不可少的。

The process of radioactive decay of nuclei has been known for some time. The usual process of decay is known as beta-decay, where the nucleus emits an energetic electron, thereby turning a neutron into a proton and, at the same time, emitting a ghostly particle called an antineutrino. This process has been measured and theoretically modeled with excellent agreement. In rare cases, some nuclei can emit two electrons simultaneously, along with two antineutrinos, in a process called double beta-decay. This process is difficult to measure, because it is so rare, and difficult to calculate because of uncertainties in the nuclear structure. The goal of this research is to reduce the uncertainties in nuclear structure by measuring nuclear reactions relevant to the double beta-decay process. This will help in the understanding of experiments on neutrinoless double beta-decay, a proposed beta-decay process in which no neutrinos are observed. The search for this elusive decay mode has been identified by the Nuclear Science Advisory Committee as one of the most important questions facing nuclear science, since those experiments would provide critical information on the fundamental properties of neutrinos and antineutrinos.One potential background contribution to experiments of double beta-decay comes from neutrons hitting either the source material or nearby shielding materials. These neutrons can create more neutrons, or can create gamma rays to mimic the desired signal. Several current experiments are studying the neutrinoless double-beta decay of isotope xenon-136. A similar isotope, xenon-134, is also present as an impurity, which was recently discovered to emit a potential background event when hit with neutrons. The research conducted with this award will investigate this recently-discovered background using a highly-enriched gaseous xenon target. The gaseous xenon sample will be irradiated with neutrons at the Triangle Universities Nuclear Laboratory, and then will be counted using a shielded high-purity germanium detector in the Low Background Counting Facility. The research performed under this award will extend our knowledge of potential double beta decay backgrounds in xenon, which will assist in planning the future ton-scale neutrinoless double beta decay experiments. Since observation of neutrinoless double beta decay is a major component of the nuclear science long-range plan, gaining information regarding backgrounds is essential.