Neutrino Geoscience: Geoneutrinos and Heat Production in the Earth

是什么驱动着板块构造、地幔对流和地球动力学？地球向太空辐射46太瓦（4600亿瓦），这种能量发射反映了原始源和放射性源的贡献，前者构成了行星吸积和核形成源。在地球内部，三种放射性元素（钾、钍和铀）的衰变产生了99%的地球？美国的核能。现有的地球中微子通量测量，即地球自然放射性产生的电子反中微子，揭示了地球上铀和钍的含量，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的放射性成因功率，而这一分量加上地幔通量约占地球损失的总功率的1/3。剩下的三分之二的地球表面热通量来自海洋之下，但不知道这些地幔通量中有多少是原始的，多少是放射性的。总的来说，地球的成分模型允许对地幔的放射性生成能力进行高达30倍的估计。了解地球的热进化史与了解地幔的总放射成因能力密切相关。因此，这个项目试图了解地球冷却的速度和幅度。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“燃料计”，以确定地球上原始燃料和放射性燃料的比例。此外，将与粒子物理学家和美国情报界的成员合作，为防止核扩散的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球中微子研究分析的背景，地球中微子是反应堆监测的背景。尽管尽了最大的努力，但考虑到地球组成的相互竞争的模型，在驱动地幔动力学的放射性成因功率的数量上仍然存在一个数量级的不确定性。对存在于地幔和大部分大陆地壳深处的放射性成因和发热元素（K、Th和U）丰度的直接测量是不存在的。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内投入使用。在接下来的8年中，一套5个实验将确定地幔对地表热损失的放射性成因贡献，当对参考模型进行测试时，这些数据可以确定来自地幔的放射性成因热。这些结果将确定硅酸盐地球组成的限制，并将为定义地幔对流模式的模型设定允许值的界限。将研究地球上产热元素的丰度和分布，主要任务包括：​4)根据对区域和全球贡献的估计，假设所有探测器看到的地幔信号大致相同（在+/-10%范围内），测试来自所有探测器的现有和未来数据；5)使用上述数据测试整体硅酸盐地球模型。从现有和计划中的探测器获得的数据可以解决地球科学中的几个主要问题，例如：1)构成地球的基本材料是什么；2)相对于吸积、岩心形成和绝灭核素的余热，现在放射性成因热的比例是多少？3)现今大陆地壳的放射性成因热相对于地幔的比例是多少；4)硅酸盐土、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、地幔对流和地球动力学的力量，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。

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.