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

位于日本中部的KamLAND探测器是测量从地球发射的中微子的最长和最大的探测器。 中微子，或地中微子，来自地球时，是非常小的，不带电的粒子，从岩石中的天然放射性释放出来。这些粒子击中任何物体的机会都很小，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。计算通过KamLAND探测器的地中微子的数量使我们能够知道地球内部的放射性供应，即使我们无法从地球深处接触到岩石。 该项目旨在研究距离探测器最近的岩石，因为这些岩石发射的地中微子对测量信号的影响大于距离较远的岩石。 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，只留下来自无法到达的地球深处的信号。 最后一个信号是地球内部放射性的指示。 这项研究是与东北大学中微子科学研究中心主任、KamLAND项目首席研究员井上邦雄教授合作进行的。地球的放射性能量并没有受到很好的限制，估计从低（10 TW）到高（30 TW）不等。 因此，测量地球的地中微子通量可以作为地球内部热量产生的替代。 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得的通量中减去地壳通量。 遗憾的是，KamLAND地壳通量的模型估计值之间存在差异。该项目将创建一个高分辨率的3D模型，该模型涵盖KamLAND（东部）周围最近300公里的地壳。~总信号的50%）。所有现有的地球化学（铀和钍）和地球物理（地震、横截面、钻孔、热流和重力）数据将被整合到一个单一的连贯和自洽的模型中。合并日本地质图上定义的单元将提供简化的储层，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，我们将根据所收集的地球化学数据来表征U和Th浓度及其不确定性。这个3D模型具有确定的物理结构和放射性元素浓度，将用于计算KamLAND的新的近场地壳地中微子信号。 东亚和太平洋夏季研究所计划下的这个奖项支持美国研究生的夏季研究，由NSF和日本科学促进会共同资助。

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.