Enriched 76Ge detectors for the MAJORANA DEMONSTRATOR

这是我们探索理解中微子的激动人心的时刻，中微子是在早期宇宙、宇宙学和天体物理学以及核物理和粒子物理学中发挥关键作用的基本粒子。中微子振荡实验的结果提供了中微子具有质量的令人信服的证据，并首次表明核物理和粒子物理的标准模型是不完整的。随着人们认识到中微子的质量很大，人们对研究中微子的本征性质越来越感兴趣。了解中微子的质量产生机制、中微子的性质(Majorana或Dirac)、绝对中微子质量标度和中微子质量谱是近期中微子实验的一些主要焦点。这一奖项的学术价值是基于这样一个事实，即对无中微子核双β衰变的敏感搜索是确定中微子是否是Majorana粒子(它们自己的反粒子)的唯一实用方法。这种奇特的衰变是对轻子数守恒最敏感的测试，轻子数守恒是基本粒子物理学中的一个重要对称性。为了最终实现使用锗(Ge)探测器的1吨规模的无中微子核双β衰变实验，Majorana合作正在组装一个被称为演示器的原型，旨在确认可以达到足够低的本底水平，以证明如此大的实验是合理的。演示器的基准计划是用富含双β同位素76-Ge的Ge制造15公斤的Ge探测器。因为这种实验的大部分成本是与之相关的仪器，而不是浓缩GE，而且因为一个人可以在不增加基本成本的情况下显著增加仪表式76-GE的质量，所以有机会以合理的增量额外成本“增加”项目的物理覆盖范围。该奖项为额外的Ge探测器提供支持，这些探测器由浓缩材料制造，以改善物理距离。广泛影响：从吨级实验开发的更大、更低本底的HPGe阵列技术有望实现新一代高效、超低本底伽马能谱测量。将受益于这一新一代技术的领域包括：暗物质直接搜索；环境监测测量；大气、海洋和地下水环境运输；放射性测年方法；反应堆监测；确定极低职业辐射暴露的生物测定；以及涉及极低放射性示踪剂的生物研究。北卡罗来纳大学与莫尔黑德天文馆合作的E&Amo项目将把地下科学带给公众。

This is an exciting time in our quest to understand neutrinos -- fundamental particles that play key roles in the early universe, in cosmology and astrophysics, and in nuclear and particle physics. Results from neutrino oscillation experiments have provided compelling evidence that neutrinos have mass and give the first indication that the Standard Model of nuclear and particle physics is incomplete. With the realization that neutrinos are massive, there is an increased interest in investigating their intrinsic properties. Understanding the neutrino mass generation mechanism, the neutrino character (Majorana or Dirac), the absolute neutrino mass scale, and the neutrino mass spectrum are some of the main focuses of the immediate future's neutrino experiments. The intellectual merit of this award is based on the fact that a sensitive search for the neutrino-less nuclear double-beta decay is the only practical way to determine if neutrinos are Majorana particles (their own antiparticles). This exotic decay is the most sensitive test of lepton-number conservation, which is an important symmetry in elementary particle physics. With the goal of ultimately realizing a 1-tonne scale neutrino-less nuclear double-beta decay experiment using Germanium (Ge) detectors, the Majorana collaboration is assembling a prototype referred to as the Demonstrator that is intended to confirm that background levels low enough to justify such a large experiment can be reached. The baseline plan for the Demonstrator is for 15 kg of Ge detectors fabricated from Ge enriched in the double-beta isotope 76-Ge. Because most of the cost of such an experiment is the apparatus associated with it and not enriched Ge, and because one can increase the mass of instrumented 76-Ge significantly without increasing that base cost, there is the opportunity to "increase" the physics reach of the project for a reasonable, incremental additional cost. This award provides support for extra Ge detectors fabricated from enriched material to improve the physics reach.Broader Impacts: The technology of larger, lower-background HPGe arrays developed from a tonne-scale experiment can be expected to enable a new generation of highly efficient, ultra-low-background gamma spectroscopy measurements. Among the fields that stand to benefit from this new generation of technology are: direct dark matter searches; measurements for environmental monitoring; atmospheric, ocean, and groundwater environmental transport; methods of radioactive dating; reactor monitoring; bioassay for determining very low occupational exposures to radiation; and biological studies involving radiotracers at very low activities. An E&O program with the Morehead Planetarium on the campus of U. of North Carolina will bring underground science to the public.