EAPSI: Understanding the Composition of the Earth by Charactering the Radioactivity of Rocks

位于日本中部的KamLAND探测器是运行时间最长、规模最大的测量地球发射中微子的探测器。来自地球的中微子是非常小的、无电荷的粒子，是由岩石内部的自然放射性释放出来的。这些粒子撞击任何物体的几率很小，因此可以很容易地从地球内部的任何地方传播到地球表面。尽管我们无法接触到地球深处的岩石，但通过KamLAND探测器计算地球中微子的数量可以让我们了解地球内部的放射性供应情况。这个项目的目的是研究离探测器最近的岩石，因为这些岩石发射的地球中微子对测量信号的影响比那些更远的岩石更大。在这项研究中，来自日本岩石的估计信号将从KamLAND的测量中减去，只留下来自难以接近的地球深处的信号。最后的信号表明了地球内部的放射性程度。这项工作是与东北大学的井上国雄教授合作进行的，他是东北大学中微子科学研究中心的主任，也是KamLAND的首席研究员。地球的产生放射性的能力没有得到很好的限制，估计从低（10太瓦）到高（30太瓦）的产热。因此，测量来自地球的地球中微子的通量可以作为地球内部产热的代理。KamLAND（日本）和Borexino（意大利）是仅有的两个运行中的探测器。确定地幔信号是一个重要的目标，需要从这些探测器测量到的通量中减去地壳通量。不幸的是，在卡姆兰的地壳通量的模型估计之间存在差异。该项目将创建KamLAND周围最近300公里地壳的高分辨率3D模型（约占总信号的50%）。所有可用的地球化学（U和Th）和地球物理（地震、剖面、井眼、热流和重力）数据将整合到一个单一的连贯和自一致的模型中。将日本地质图上定义的单元进行整合将提供简化的储层，这些储层可以通过日本中部的地球物理数据进行三维定义。对于这些储层，我们将从组合的地球化学数据中描述U和Th的浓度及其不确定度。这个三维模型具有明确的物理结构和放射性元素浓度，将用于计算KamLAND的一个新的近场地壳中微子信号。该奖项隶属于东亚和太平洋暑期研究所项目，由美国国家科学基金会和日本科学促进会共同资助，支持一名美国研究生进行暑期研究。

The KamLAND detector in central Japan is the longest running and largest detector measuring neutrinos emitted from the Earth. Neutrinos, or geoneutrinos when from the Earth, are incredibly small, chargeless particles emitted from natural radioactivity within rocks. These particles have a very small chance of hitting anything, and can thus travel easily from anywhere inside the Earth to the surface. Counting the number of geoneutrinos passing through the KamLAND detector allows us to know the supply of radioactivity within the Earth, even though we cannot access rocks from the deep Earth. This project aims to investigate the rocks closest to the detector, as the geoneutrinos emitted by these rocks have a larger effect on the measured signal vs those farther away. The estimated signal from Japanese rocks in this study will be subtracted from the measurement by KamLAND, leaving only the signal from the inaccessible deep Earth. The final signal is indicative of the amount of radioactivity within the Earth. This work is being conducted in conjunction with Professor Kunio Inoue at Tohoku University, who is the Director of the Research Center of Neutrino Sciences at Tohoku University and principal investigator of KamLAND.The radiogenic power of the Earth is not well constrained, with estimates ranging from low (10 TW) to high (30 TW) heat production. Measurement of the flux of geoneutrinos from the Earth thus acts as a proxy for the heat production within the Earth. KamLAND (Japan) and Borexino (Italy) are the only two operating detectors. Determining the mantle signal, an important objective, requires subtraction of the crustal flux from the measured flux at these detectors. Unfortunately, discrepancy exists between model estimates of the crustal flux at KamLAND. This project will create a high-resolution, 3D model of the nearest 300 km of crust surrounding KamLAND (est. ~ 50% of total signal). All available geochemical (U and Th) and geophysical (seismic, cross-sections, borehole, heat flow, and gravity) data will be integrated into a single coherent and self-consistent model. Consolidation of units defined on a geologic map of Japan will provide simplified reservoirs, which can be defined 3-dimensionally by the assembled geophysical data in Central Japan. To these reservoirs we will characterized the U and Th concentrations, and their uncertainties, from the assembled geochemical data. This 3D model, with defined physical structure and radioactive element concentration, will be used to calculate a new near-field, crustal geoneutrino signal at KamLAND. This award under the East Asia and Pacific Summer Institutes program supports summer research by a U.S. graduate student and is jointly funded by NSF and the Japan Society for the Promotion of Science.