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

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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.