Geoneutrino Flux Research Articles

Frontier of Understanding Earth's Dynamics

Frontier of Understanding Earth's Dynamics

Quantifying Earth's radiogenic heat budget

Earth's internal heat drives its dynamic engine, causing mantle convection, plate tectonics, and the geodynamo. These renewing and protective processes, which make Earth habitable, are fueled by primordial and radiogenic heat. For the past two decades, particle physicists have measured the flux of geoneutrinos, electron antineutrinos emitted during β− decay. These ghost-like particles provide a direct measure of the amount of heat producing elements (HPE: Th & U) in the Earth and in turn define the planet's absolute concentration of the refractory elements. The geoneutrino flux has contributions from the lithosphere and mantle. Detector sensitivity follows a 1/r2 (source detector separation distance) dependence. Accordingly, an accurate geologic model of the Near-Field Lithosphere (NFL, closest 500 km) surrounding each experiment is required to define the mantle's contribution. Because of its proximity to the detector and enrichment in HPEs, the local lithosphere contributes ∼50% of the signal and has the greatest effect on interpreting the mantle's signal.We re-analyzed the upper crustal compositional model used by Agostini et al. (2020) for the Borexino experiment. We documented the geology of the western Near-Field region as rich in potassic volcanism, including some centers within 50 km of the detector. In contrast, the Agostini study did not include these lithologies and used only a HPE-poor, carbonate-rich, model for upper crustal rocks in the surrounding ∼150 km of the Borexino experiment. Consequently, we report 3× higher U content for the local upper crust, which produces a 200% decrease in Earth's radiogenic heat budget, when compared to their study. Results from the KamLAND and Borexino geoneutrino experiments are at odds with one another and predict mantle compositional heterogeneity that is untenable. Combined analyses of the KamLAND and Borexino experiments using our revised local models strongly favor an Earth with ∼20 TW present-day total radiogenic power. The next generation of geoneutrino detectors (SNO+, counting; and JUNO, under construction) will better constrain the HPE budget of the Earth.

What can the CNO neutrinos flux measurement done by Borexino say about 40K geoneutrino flux?

Borexino collaboration announced the observation of CNO neutrinos flux. Its value appeared larger than expected in case of the Sun high metallicity model. This could be regarded as evidence of large potassium content inside the Earth. The potassium abundance can reach (1.5 ± 1.0)% in the whole Earth and the Earth heat flux can be at the level of 200-300 TW. To resolve the problem a new experiment is demanded with a detector similar to Borexino one but better in backgrounds or a detector with another techniques of neutrino measurement, for example on base of 115In.

Geoneutrinos from the rock overburden at SNO+

SNOLAB is one of the deepest underground laboratory in the world with an overburden of 2092 m. The SNO+ detector is designed to achieve several fundamental physics goals as a low-background experiment, particularly measuring the Earth’s geoneutrino flux. Here we evaluate the effect of the 2 km overburden on the predicted crustal geoneutrino signal at SNO+. A refined 3D model of the 50 χ 50 km upper crust surrounding the detector and a full calculation of survival probability are used to model the U and Th geoneutrino signal. Comparing this signal with that obtained by placing SNO+ at sea level, we highlight a 1.4+1.8-0.9 TNU signal difference, corresponding to the ~5% of the total crustal contribution. Finally, the impact of the additional crust extending from sea level up to ~300 m was estimated.

Non-negligible oscillation effects in the crustal geoneutrino calculations

An accurate prediction of the geo-neutrino signal from the crust serves as a necessary prerequisite in the determination of the geo-neutrino flux from the mantle. In this work we report the non-negligible effect associated to the exact three-flavor antineutrino survival probability in the calculation of the crustal geo-neutrino signal, which was usually approximated as a constant average in previous studies. A geo-neutrino signal underestimation of about 1-2 TNU is observed as a result of the oscillatory behaviour within the local crustal region extending for about 300 km from the experimental site. We also estimated that the Mikheyev-Smirnov-Wolfenstein matter oscillation is responsible for a $0.1\%$-$0.3\%$ increase of the local crustal signal, depending on the detector location. This work reminds that the exact oscillation possibility in matter should be considered for future prediction of the local crustal geo-neutrino signal.

JULOC: A local 3-D high-resolution crustal model in South China for forecasting geoneutrino measurements at JUNO

Geothermal energy is one of the keys for understanding the mechanisms driving the plate tectonics and mantle dynamics. The surface heat flux, as measured in boreholes, provides limited insights into the relative contributions of primordial versus radiogenic sources of the interior heat budget. Geoneutrino, electron antineutrino that is produced from the radioactive decay of the heat producing elements, is a unique probe to obtain direct information about the amount and distribution of heat producing elements in the crust and mantle. Cosmochemical, geochemical, and geodynamic compositional models of the Bulk Silicate Earth (BSE) individually predict different mantle neutrino fluxes, and therefore may be distinguished by the direct measurement of geoneutrinos. Due to low counting statistics, the results from geoneutrino measurements at several sites are inadequate to resolve the geoneutrino flux. However, the JUNO detector, currently under construction in South China, is expected to provide an exciting opportunity to obtain a highly reliable statistical measurement, which will produce sufficient data to address several vital questions of geological importance.However, the detector cannot separate the mantle contribution from the crust contribution. To test different compositional models of the mantle, an accurate a-priori estimation of the crust geoneutrino flux based on a three-dimensional (3-D) crustal model is important. This paper presents a 3-D crustal model over a surface area of 10° × 10° grid surrounding the JUNO detector and a depth down to the Moho discontinuity, based on the geological, geophysical and geochemical properties. This model provides a distinction of the thickness of the different crustal layers together with the corresponding Th and U abundances. We also present our predicted local contribution to the total geoneutrino flux and the corresponding radiogenic heat. Compared to previous studies where the surface layer is subdivided into a few geologic units and each of them is considered to have the same geochemical property, our method has provided an effective approach to reduce the uncertainty of geoneutrino flux prediction by constructing the composition of the surface layer through cell by cell which are independent to each other.

Stochastic modeling of 3-D compositional distribution in the crust with Bayesian inference and application to geoneutrino observation in Japan

Geoneutrino observations, first achieved by KamLAND in 2005 and followed by Borexino in 2010, have accumulated statistics and improved sensitivity for more than ten years. The uncertainty of the geoneutrino flux at the surface is now reduced to a level small enough to set useful constraints on U and Th abundances in the Bulk Silicate Earth (BSE). However, in order to make inferences on earth’s compositional model, the contributions from the local crust need to be understood within a similar uncertainty. Here we develop a new method to construct a stochastic crustal composition model utilizing Bayesian inference. While the methodology has general applicability, it incorporates all the local uniqueness in its probabilistic framework. Unlike common approaches for this type of problem, our method does not depend on crustal segmentation into upper, (middle) and lower, whose classification and boundaries are not always well defined. We also develop a new modeling method to infer rock composition distributions that conserve mass balance and therefore do not bias the results. Combined with a new vast collection of geochemical data for rock samples in the Japan arc, we apply this method to geoneutrino observation at Kamioka, Japan. Currently a difficulty remains in the handling of correlations in the flux integration; we conservatively assume maximum correlation, which leads to large flux estimation errors of 60–70%. Despite the large errors, this is the first local crustal model for geoneutrino flux prediction with probabilistic error estimation in a reproducible way.

Study of Earth’s Heat Flux by Means of Geoneutrino Detection

The heat flux from the Earth’s interior and its connection with the number of neutrinos recorded by detectors at the Earth’s surface are discussed. The values predicted for the geoneutrino fluxes may be matched with experimental data, but the observed flux of the Earth’s internal heat requires the presence of a larger amount of radioactive elements. The amount of uranium and thorium within the Earth is constrained by measurements performed with the aid of modern geoneutrino detectors. This makes it possible to explain completely a flux of 50 TW. There are indications that the flux from the Earth’s interior is 200 to 250 TW. Such a flux could be explained only by the presence of a substantially larger amount of potassium in the Earth. In order to determine precisely the heat flux from the Earth’s interior, it is necessary to measure completely the flux of antineutrinos from all heat-releasing isotopes, including the flux of neutrinos from 40K decay. Possibly, this flux has already been observed at the Borexino detector.

Geoneutrino : experimental status and perspectives

The current results of the Borexino and KamLAND on geoneutrino are presented and the perspectives for measurement of geoneutrino fluxes both on existing and planned detectors are discussed. We discuss also the nuclear physics inputs relevant for precision measurement of the geoneutrino fluxes.

Geo-Neutrinos and the Earth’s Internal Heat Flux

Predictions of geo-neutrino fluxes and the Earth’s internal heat flux made by the Hydride Earth model are discussed. The prediction of geo-neutrino fluxes can be consistent with experimental measured fluxes. The predicted value of the Earth’s internal heat flux is significantly larger than the value experimentally obtained under the assumption that the main mode of heat transport is thermal conductivity. We consider another mode of heat transport in the Earth’s crust: heat transport by hot gases created in the Earth’s crust at great depth. We discuss also experimental data supporting this idea, particularly the temperature profiles obtained in the Kola superdeep borehole.

Geo-neutrino, Earth heat flux, Earth electricity

We discussed the idea of big value of potassium abundance in the Earth. We showed that Borexino single event spectrum permit the potassium abundance up to 2% instead of the CNO neutrino flux contribution. Works [5], [6] introduce the idea that fast α particles are appeared in nuclear processes in solar core plasma. The reactions of these α particles with CNO nuclei can suppress the CNO neutrino flux. We demonstrated the connection between the existence of Earth’s electric field and the big value of 40K geo-neutrino flux because the both phenomena are the sequences from Hydride Earth model.

How Geoneutrinos can help in understanding of the Earth heat flux

The Hydride Earth model predictions of geoneutrino flux and intrinsic Earth heat flux are discussed. The geoneutrino flux predicted by the model can be adjusted to the experimental one. The predicted intrinsic Earth heat flux is significantly larger than model dependent experimental value obtained under assumption that the main heat transfer mechanism is a thermal conductivity. We introduce an additional mechanism of heat transfer in the Earth’s crust, namely the energy transfer by hot gases produced in the Earth crust at great depths. The experimental data supporting this idea, in particular the temperature profiles measured in the Kola super deep borehole, are discussed.

Exploring the hidden interior of the Earth with directional neutrino measurements

Roughly 40% of the Earth’s total heat flow is powered by radioactive decays in the crust and mantle. Geo-neutrinos produced by these decays provide important clues about the origin, formation and thermal evolution of our planet, as well as the composition of its interior. Previous measurements of geo-neutrinos have all relied on the detection of inverse beta decay reactions, which are insensitive to the contribution from potassium and do not provide model-independent information about the spatial distribution of geo-neutrino sources within the Earth. Here we present a method for measuring previously unresolved components of Earth’s radiogenic heating using neutrino-electron elastic scattering and low-background, direction-sensitive tracking detectors. We calculate the exposures needed to probe various contributions to the total geo-neutrino flux, specifically those associated to potassium, the mantle and the core. The measurements proposed here chart a course for pioneering exploration of the veiled inner workings of the Earth.

Geoneutrinos at Jinping: Flux prediction and oscillation analysis

Geoneutrinos are electron antineutrinos ($\bar\nu_e$) generated by the beta-decays of radionuclides naturally occurring inside the Earth, in particular $^{238}$U, $^{232}$Th, and $^{40}$K. Measurement of these neutrinos provides powerful constraints on the radiogenic heat of the Earth and tests on the Earth models. Since the prediction of $\bar\nu_e$'s in geoneutrino flux is subject to neutrino oscillation effects, we performed a calculation including detailed oscillation analysis in the propagation of geoneutrinos and reactor neutrinos generated around the Earth. The expected geoneutrino signal, the reactor neutrino background rates and the systematic error budget are provided for a proposed 3-kiloton neutrino detector at the Jinping underground lab in Sichuan, China. In addition, we evaluated sensitivities for the geoneutrino flux, Th/U ratio and power of a possible fission reactor in the interior of Earth.

Physics prospects of the Jinping neutrino experiment**Supported by the National Natural Science Foundation of China (11235006, 11475093, 11135009, 11375065, 11505301, and 11620101004), the Tsinghua University Initiative Scientific Research Program (20121088035, 20131089288, and 20151080432), the Key Laboratory of Particle & Radiation Imaging (Tsinghua University), the CAS Center for Excellence in Particle Physics (CCEPP), U.S. National Science Foundation Grant PHY-1404311 (Beacom), and

The China Jinping Underground Laboratory (CJPL), which has the lowest cosmic-ray muon flux and the lowest reactor neutrino flux of any laboratory, is ideal to carry out low-energy neutrino experiments. With two detectors and a total fiducial mass of 2000 tons for solar neutrino physics (equivalently, 3000 tons for geo-neutrino and supernova neutrino physics), the Jinping neutrino experiment will have the potential to identify the neutrinos from the CNO fusion cycles of the Sun, to cover the transition phase for the solar neutrino oscillation from vacuum to matter mixing, and to measure the geo-neutrino flux, including the Th/U ratio. These goals can be fulfilled with mature existing techniques. Efforts on increasing the target mass with multi-modular neutrino detectors and on developing the slow liquid scintillator will increase the Jinping discovery potential in the study of solar neutrinos, geo-neutrinos, supernova neutrinos, and dark matter.

Revealing the Earth’s mantle from the tallest mountains using the Jinping Neutrino Experiment

The Earth’s engine is driven by unknown proportions of primordial energy and heat produced in radioactive decay. Unfortunately, competing models of Earth’s composition reveal an order of magnitude uncertainty in the amount of radiogenic power driving mantle dynamics. Recent measurements of the Earth’s flux of geoneutrinos, electron antineutrinos from terrestrial natural radioactivity, reveal the amount of uranium and thorium in the Earth and set limits on the residual proportion of primordial energy. Comparison of the flux measured at large underground neutrino experiments with geologically informed predictions of geoneutrino emission from the crust provide the critical test needed to define the mantle’s radiogenic power. Measurement at an oceanic location, distant from nuclear reactors and continental crust, would best reveal the mantle flux, however, no such experiment is anticipated. We predict the geoneutrino flux at the site of the Jinping Neutrino Experiment (Sichuan, China). Within 8 years, the combination of existing data and measurements from soon to come experiments, including Jinping, will exclude end-member models at the 1σ level, define the mantle’s radiogenic contribution to the surface heat loss, set limits on the composition of the silicate Earth, and provide significant parameter bounds for models defining the mode of mantle convection.

Potential of geo-neutrino measurements at JUNO**Supported in part by National Natural Science Foundation of China (11405056, 11305193, 11205176, 21504063), National Science Foundation of U.S. (EAR 1067983/1068097), Strategic Priority Research Program of the Chinese Academy of Sciences under Grant No. XDA10010100 and CAS Center for Excellence in Particle Physics (CCEPP)

The flux of geoneutrinos at any point on the Earth is a function of the abundance and distribution of radioactive elements within our planet. This flux has been successfully detected by the 1-kt KamLAND and 0.3-kt Borexino detectors, with these measurements being limited by their low statistics. The planned 20-kt JUNO detector will provide an exciting opportunity to obtain a high statistics measurement, which will provide data to address several questions of geological importance. This paper presents the JUNO detector design concept, the expected geo-neutrino signal and corresponding backgrounds. The precision level of geo-neutrino measurements at JUNO is obtained with the standard least-squares method. The potential of the Th/U ratio and mantle measurements is also discussed.

AGM2015: Antineutrino Global Map 2015.

Every second greater than 1025 antineutrinos radiate to space from Earth, shining like a faint antineutrino star. Underground antineutrino detectors have revealed the rapidly decaying fission products inside nuclear reactors, verified the long-lived radioactivity inside our planet, and informed sensitive experiments for probing fundamental physics. Mapping the anisotropic antineutrino flux and energy spectrum advance geoscience by defining the amount and distribution of radioactive power within Earth while critically evaluating competing compositional models of the planet. We present the Antineutrino Global Map 2015 (AGM2015), an experimentally informed model of Earth’s surface antineutrino flux over the 0 to 11 MeV energy spectrum, along with an assessment of systematic errors. The open source AGM2015 provides fundamental predictions for experiments, assists in strategic detector placement to determine neutrino mass hierarchy, and aids in identifying undeclared nuclear reactors. We use cosmochemically and seismologically informed models of the radiogenic lithosphere/mantle combined with the estimated antineutrino flux, as measured by KamLAND and Borexino, to determine the Earth’s total antineutrino luminosity at . We find a dominant flux of geo-neutrinos, predict sub-equal crust and mantle contributions, with ~1% of the total flux from man-made nuclear reactors.

Expected geoneutrino signal at JUNO

Constraints on the Earth’s composition and on its radiogenic energy budget come from the detection of geoneutrinos. The Kamioka Liquid scintillator Antineutrino Detector (KamLAND) and Borexino experiments recently reported the geoneutrino flux, which reflects the amount and distribution of U and Th inside the Earth. The Jiangmen Underground Neutrino Observatory (JUNO) neutrino experiment, designed as a 20 kton liquid scintillator detector, will be built in an underground laboratory in South China about 53 km from the Yangjiang and Taishan nuclear power plants, each one having a planned thermal power of approximately 18 GW. Given the large detector mass and the intense reactor antineutrino flux, JUNO aims not only to collect high statistics antineutrino signals from reactors but also to address the challenge of discriminating the geoneutrino signal from the reactor background. The predicted geoneutrino signal at JUNO is $$ {39.7}_{-5.2}^{+6.5} $$ terrestrial neutrino unit (TNU), based on the existing reference Earth model, with the dominant source of uncertainty coming from the modeling of the compositional variability in the local upper crust that surrounds (out to approximately 500 km) the detector. A special focus is dedicated to the 6° × 4° local crust surrounding the detector which is estimated to contribute for the 44% of the signal. On the basis of a worldwide reference model for reactor antineutrinos, the ratio between reactor antineutrino and geoneutrino signals in the geoneutrino energy window is estimated to be 0.7 considering reactors operating in year 2013 and reaches a value of 8.9 by adding the contribution of the future nuclear power plants. In order to extract useful information about the mantle’s composition, a refinement of the abundance and distribution of U and Th in the local crust is required, with particular attention to the geochemical characterization of the accessible upper crust where 47% of the expected geoneutrino signal originates and this region contributes the major source of uncertainty.

Geo-neutrinos and Earth Models

We present the current status of geo-neutrino measurements and their implications for radiogenic heating in the mantle. Earth models predict different levels of radiogenic heating and, therefore, different geo-neutrino fluxes from the mantle. Seismic tomography reveals features in the deep mantle possibly correlated with radiogenic heating and causing spatial variations in the mantle geo-neutrino flux at the Earth surface. An ocean-based observatory offers the greatest sensitivity to the mantle flux and potential for resolving Earth models and mantle features. Refinements to estimates of the geo-neutrino flux from continental crust reduce uncertainty in measurements of the mantle flux, especially measurements from land-based observatories. These refinements enable the resolution of Earth models using the combined measurements from multiple continental observatories.