Enriched 76Ge detectors for the MAJORANA DEMONSTRATOR

这是一个令人兴奋的时刻，在我们寻求了解中微子-基本粒子，发挥关键作用，在早期宇宙，宇宙学和天体物理学，核和粒子物理学。中微子振荡实验的结果提供了令人信服的证据，证明中微子有质量，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，人们对研究它们的内在性质越来越感兴趣。理解中微子质量产生机制、中微子性质（马约拉纳或狄拉克）、绝对中微子质量标度和中微子质谱是近期中微子实验的一些主要焦点。这个奖项的学术价值是基于这样一个事实，即对中微子较少的核双β衰变的敏感搜索是确定中微子是否是马约拉纳粒子（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重要的对称性。为了最终实现使用锗（Ge）探测器进行1吨级无中微子核双β衰变实验的目标，Majorana合作正在组装一个被称为Demonstrator的原型，旨在确认背景水平足够低，可以达到这样一个大型实验。演示器的基线计划是用富含双β同位素76-Ge的Ge制造15公斤Ge探测器。因为这种实验的大部分成本是与之相关的设备而不是富集的Ge，并且因为可以在不增加基本成本的情况下显著增加仪器化的76-Ge的质量，所以有机会“增加”项目的物理范围以获得合理的增量额外成本。更广泛的影响：从吨级实验中开发出的更大、更低背景的HPGe阵列技术有望实现新一代高效、超低背景的伽马能谱测量。将受益于这一新一代技术的领域包括：直接暗物质搜索;环境监测测量;大气、海洋和地下水环境迁移;放射性定年方法;反应堆监测;确定极低职业辐射照射的生物测定;以及涉及极低放射性示踪剂的生物研究。一个与莫尔黑德天文馆合作的地球观测项目。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.