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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.

是什么为板块构造、地幔对流和地球发电机提供动力？地球向太空辐射46太瓦（4600万千瓦），这种功率发射反映了原始和辐射源的贡献，前者构成行星吸积和核心形成源。在地球内部，三种放射性元素（钾、钍和铀）的衰变产生了地球的99%？的核力量。地球中微子（地球天然放射性的电子反中微子）通量的现有测量揭示了地球中铀和钍的含量，但这些数据具有相当大的不确定性。鉴于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7 TW的放射性能量，该分量加上下伏地幔通量约占地球总能量损失的1/3。地球表面热通量的其余2/3来自海洋之下，但不知道这些地幔通量中有多少是原始的还是辐射成因的贡献。地球的组成模型共同允许高达30的因素，估计地幔的放射性力量。了解地球的热演化历史与了解地幔的总辐射成因能力密切相关。因此，该项目试图了解地球正在冷却的速度和幅度。因此，通过确定为地球发动机提供动力的放射性能量的数量，人们可以制作一个“燃料表”，以确定地球上原始燃料与放射性燃料的比例。此外，还将与粒子物理学家和美国情报界成员合作，为核不扩散目的探测电子反中微子（来自核反应堆和地球）。反应堆反中微子是地中微子研究分析的背景，地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竞争模型，驱动地幔动力学的放射性能量的数量仍然存在数量级的不确定性。对地幔和大部分大陆深部地壳中放射性发热元素（K、Th和U）丰度的直接测量尚不存在。重要的是，这种情况正在迅速改变，因为新的，更大和更灵敏的地中微子探测器将在未来几年上线。在接下来的8年里，一套5个实验将确定地幔的辐射成因对地表热损失的贡献，当测试到参考模型时，这些数据可以确定来自地幔的辐射成因热。这些结果将确定硅酸盐地球成分的限度，并将确定确定地幔对流模式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）改进预测并减少在向SNO+探测器定义区域地中微子信号时的系统误差（安大略，加拿大），2）围绕KamLAND，JUNO的区域岩性的模型地质、地球化学和地球物理数据（中国广州）和金平（中国四川）探测器，以改善地质预测，3）开发和改进1x 1度尺度的全球参考模型，使其成为超越地中微子研究应用的社区资源，4）根据对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，假设所有探测器都看到大致相同的地幔信号（± 10%以内）; 5）利用上述数据对块状硅酸盐地球模型进行测试。目前和计划中的探测器提供的数据可以解决地球科学中的几个主要问题，例如：（1）构成地球的基本成分是什么;（2）相对于吸积、地核形成和消失的核素的余热，目前放射性成因热的比例是多少;（3）相对于地幔中的放射性成因热，目前大陆地壳中的放射性成因热的比例是多少;（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力量，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。