权益分类	功能权益	普通用户	{{item.name}}会员
{{category.name}}	{{benefitItem.name}}

Neutrino Geoscience: Geoneutrinos and Heat Production in the Earth

中微子地球科学：地中微子和地球产热

基本信息

批准号：
1650365
负责人：
William McDonough
金额：
$ 29.91万
依托单位：
University of Maryland, College Park
依托单位国家：
美国
项目类别：
Continuing Grant
财政年份：
2017
资助国家：
美国
起止时间：
2017-04-01 至 2021-09-30
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1650365&HistoricalAwards=false
关键词：
Neutrino Geoscience Geoneutrinos Heat Production

项目摘要

What powers plate tectonics, mantle convection, and the Earth's geodynamo? The Earth radiates 46 terawatts (46 million millon watts) to space, and this power emission reflects contributions from primordial and radiogenic sources, with the former constituting planetary accretion and core-formation sources. Inside the Earth, the decay of 3 radioactive elements (potassium, thorium, and uranium) produces 99% of the Earth?s nuclear power. Existing measurements of the Earth's flux of geoneutrinos, electron antineutrinos from terrestrial natural radioactivity, reveal the amount of uranium and thorium in the Earth, but these data come with considerable uncertainty. Given the understanding of the amount and distribution of these elements in the continental crust, it is known that they contribute about 7 TW of radiogenic power to the continental heat flux, and this component plus an underlying mantle flux accounts for about 1/3 of the total power lost from the Earth. The remaining 2/3 of the Earth's surface heat flux comes up beneath the oceans, but it is not known how much of this mantle flux is primordial versus radiogenic contributions. Compositional models of the Earth collectively allow for up to a factor of 30 in estimates of the mantle's radiogenic power. The understanding of the Earth's thermal evolutionary history is intimately linked to knowing the total radiogenic power of the mantle. Consequently, this project seeks to understand the rate and magnitude by which the planet is cooling. Thus, by determining the amount of radioactive energy that powers the Earth's engine, one can make a 'fuel gauge' that identifies the proportion of primordial to radioactive fuel left in the planet. In addition, there will be collaboration with particle physicists and members of the U.S. intelligence community in the detection of electron antineutrinos (from nuclear reactors and the Earth) for nuclear nonproliferation purposes. Reactor antineutrinos are the background for the analyses of geoneutrino research and geoneutrinos are the background for reactor monitoring.Despite best efforts there remains an order of magnitude uncertainty in the amount of radiogenic power driving mantle dynamics, given the competing models of the Earth's composition. Direct measurements of the abundance of radiogenic, heat-producing elements (K, Th and U) present in the mantle and much of the deep continental crust do not exist. Importantly, this picture is rapidly changing because of new, larger and more sensitive geoneutrino detectors that are coming on line in the coming years. In the next 8 years, a suite of 5 experiments will define the mantle's radiogenic contribution to the surface heat loss and when tested to a reference model these data can define the radiogenic heat from the mantle. These results will fix limits on the composition of the silicate Earth and will set bounds on permissible values for models defining the mode of mantle convection.The abundance and distribution of the heat-producing elements in the Earth will be studied, and the major tasks include: 1) Improve predictions and reduce systematic errors in defining the regional geoneutrino signal to SNO+ detector (Ontario, Canada), 2) Model geological, geochemical, and geophysical data of the regional lithologies surrounding the KamLAND, JUNO (Guangzhou, China) and Jinping (Sichuan, China) detectors to improve geological predictions, 3) Develop and improve the global reference model at the 1x1 degree scale, making it a community resource that goes beyond applications in geoneutrino studies, 4) Test existing and future data from all detectors against estimates of the regional and global contribution, assuming all detectors see approximately the same mantle signal (within +/-10%), and 5) Use above data to test models of the bulk silicate Earth. Data from current and planned detectors can bring resolution to several major issues in Earth sciences, such as 1) what are the building blocks used to make the planet; 2) what is the present-day proportion of radiogenic heat relative to the residual heat of accretion, core formation and extinct nuclides; 3) what is the present-day fraction of radiogenic heat in the continental crust relative to that in the mantle; and 4) what is the composition of the silicate Earth, upper mantle, and lower mantle? Answers to these questions will, in turn, define the power that is driving plate tectonics, mantle convection and the geodynamo, as well as the structure of mantle convection. Neutrino geoscience offers a great potential to address these broad interdisciplinary issues.

是什么推动了板块构造、地幔对流和地球的地球发电机？地球向太空辐射46太瓦特(4600万兆瓦)，这种能量发射反映了原始和放射源的贡献，前者构成行星吸积源和核心形成源。在地球内部，三种放射性元素(钾、钍和铀)的衰变产生了地球99%的能量--S核电。现有的地球中微子流量测量，即地球天然放射性的电子反中微子，揭示了地球上铀和钍的数量，但这些数据具有相当大的不确定性。根据对这些元素在大陆地壳中的数量和分布的了解，已知它们为大陆热通量贡献了约7TW的辐射成因功率，这一分量加上下伏的地幔通量约占地球总损失功率的1/3。剩下的地球表面热流的2/3来自海洋以下，但目前尚不清楚这些地幔热流中有多少是原始的相对于辐射成因的贡献。在估算地幔辐射能力时，地球的成分模型总共允许高达30倍的系数。了解地球的热演化历史与了解地幔的总辐射产生能力密切相关。因此，这个项目试图了解地球冷却的速度和程度。因此，通过确定为地球发动机提供动力的放射性能量的量，人们可以制造一个“燃料表”，来识别地球上剩余的原始燃料和放射性燃料的比例。此外，还将与粒子物理学家和美国情报界成员合作，探测用于核不扩散目的的电子反中微子(来自核反应堆和地球)。反应堆反中微子是分析地球中微子研究的背景，地球中微子是反应堆监测的背景。尽管尽了最大努力，但考虑到地球组成的相互竞争的模型，辐射成因驱动地幔动力学的量仍然存在数量级的不确定性。目前还不存在直接测量地幔和大部分大陆深部地壳中存在的放射成因、产热元素(K、Th和U)丰度的方法。重要的是，这种情况正在迅速改变，因为新的、更大、更灵敏的地球中微子探测器将在未来几年上线。在接下来的8年里，一系列5个实验将确定地幔对地表热损失的辐射成因贡献，当对参考模型进行测试时，这些数据可以定义来自地幔的辐射成因热。这些结果将确定硅酸盐地球组成的界限，并将设定定义地幔对流模式的模型的允许值的界限。将研究地球中产热元素的丰度和分布，主要任务包括：1)改进预测并减少定义给SNO+探测器的区域地球中微子信号的系统误差；2)模拟卡姆兰德、朱诺(广州，中国)和金平(四川，中国)探测器周围的区域岩性的地质、地球化学和地球物理数据，以改进地质预测；3)开发和改进1x1度尺度的全球参考模型，使其成为超越地球中微子研究应用的社区资源，4)根据区域和全球贡献的估计，测试来自所有探测器的现有和未来数据，假设所有探测器看到大致相同的地幔信号(在+/-10%以内)，以及5)使用上述数据来测试块状硅酸盐地球的模型。来自现有的和计划中的探测器的数据可以为地球科学中的几个主要问题带来解决方案，例如：1)构成地球的积木是什么；2)今天的辐射成因热相对于吸积、核形成和灭绝的核素的剩余热的比例是多少；3)今天大陆地壳中的辐射成因热相对于地幔的比例是多少；以及4)硅酸盐地球、上地幔和下地幔的组成是什么？这些问题的答案将反过来定义驱动板块构造、地幔对流和地球发电机的动力，以及地幔对流的结构。中微子地球科学为解决这些广泛的跨学科问题提供了巨大的潜力。