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A future large-volume liquid scintillator detector such as the proposed 50 kton LENA (Low Energy Neutrino Astronomy) detector would provide a high-statistics measurement of terrestrial antineutrinos originating from $beta$-decays of the uranium and thorium chains. Additionally, the neutron is scattered in the forward direction in the detection reaction $bar u_e+pto n+e^+$. Henceforth, we investigate to what extent LENA can distinguish between certain geophysical models on the basis of the angular dependence of the geoneutrino flux. Our analysis is based on a Monte-Carlo simulation with different levels of light yield, considering an unloaded PXE scintillator. We find that LENA is able to detect deviations from isotropy of the geoneutrino flux with high significance. However, if only the directional information is used, the time required to distinguish between different geophysical models is of the order of severals decades. Nonetheless, a high-statistics measurement of the total geoneutrino flux and its spectrum still provides an extremely useful glance at the Earths interior.
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A future large-volume liquid scintillator detector would provide a high-statistics measurement of terrestrial antineutrinos originating from $beta$-decays of the uranium and thorium chains. In addition, the forward displacement of the neutron in the detection reaction $bar u_e+pto n+e^+$ provides directional information. We investigate the requirements on such detectors to distinguish between certain geophysical models on the basis of the angular dependence of the geoneutrino flux. Our analysis is based on a Monte-Carlo simulation with different levels of light yield, considering both unloaded and gadolinium-loaded scintillators. We find that a 50 kt detector such as the proposed LENA (Low Energy Neutrino Astronomy) will detect deviations from isotropy of the geoneutrino flux significantly. However, with an unloaded scintillator the time needed for a useful discrimination between different geophysical models is too large if one uses the directional information alone. A Gd-loaded scintillator improves the situation considerably, although a 50 kt detector would still need several decades to distinguish between a geophysical reference model and one with a large neutrino source in the Earths core. However, a high-statistics measurement of the total geoneutrino flux and its spectrum still provides an extremely useful glance at the Earths interior.
Decays of radionuclides throughout the Earths interior produce geothermal heat, but also are a source of antineutrinos. The (angle-integrated) geoneutrino flux places an integral constraint on the terrestrial radionuclide distribution. In this paper, we calculate the angular distribution of geoneutrinos, which opens a window on the differential radionuclide distribution. We develop the general formalism for the neutrino angular distribution, and we present the inverse transformation which recovers the terrestrial radioisotope distribution given a measurement of the neutrino angular distribution. Thus, geoneutrinos not only allow a means to image the Earths interior, but offering a direct measure of the radioactive Earth, both (1) revealing the Earths inner structure as probed by radionuclides, and (2) allowing for a complete determination of the radioactive heat generation as a function of radius. We present the geoneutrino angular distribution for the favored Earth model which has been used to calculate geoneutrino flux. In this model the neutrino generation is dominated by decays in the Earths mantle and crust; this leads to a very ``peripheral angular distribution, in which 2/3 of the neutrinos come from angles > 60 degrees away from the downward vertical. We note the possibility of that the Earths core contains potassium; different geophysical predictions lead to strongly varying, and hence distinguishable, central intensities (< 30 degrees from the downward vertical). Other uncertainties in the models, and prospects for observation of the geoneutrino angular distribution, are briefly discussed. We conclude by urging the development and construction of antineutrino experiments with angular sensitivity. (Abstract abridged.)
The large-volume liquid-scintillator detector LENA (Low Energy Neutrino Astronomy) has been proposed as a next-generation experiment for low-energy neutrinos. High-precision spectroscopy of solar, Supernova and geo-neutrinos provides a new access to the otherwise unobservable interiors of Earth, Sun and heavy stars. Due to the potent background discrimination, the detection of the Diffuse Supernova Neutrino Background is expected for the first time in LENA. The sensitivity of the proton lifetime for the decay into Kaon and antineutrino will be increased by an order of magnitude over existing experimental limits. Recent studies indicate that liquid-scintillator detectors are capable to reconstruct neutrino events even at GeV energies, providing the opportunity to use LENA as far detector in a long-baseline neutrino beam experiment.
The deepest hole that has ever been dug is about 12 km deep. Geochemists analyze samples from the Earths crust and from the top of the mantle. Seismology can reconstruct the density profile throughout all Earth, but not its composition. In this respect, our planet is mainly unexplored. Geo-neutrinos, the antineutrinos from the progenies of U, Th and K40 decays in the Earth, bring to the surface information from the whole planet, concerning its content of natural radioactive elements. Their detection can shed light on the sources of the terrestrial heat flow, on the present composition, and on the origins of the Earth. Geo-neutrinos represent a new probe of our planet, which can be exploited as a consequence of two fundamental advances that occurred in the last few years: the development of extremely low background neutrino detectors and the progress on understanding neutrino propagation. We review the status and the prospects of the field.
Superionic hydrogen was previously thought to be an exotic state predicted and confirmed only in pure H2O ice. In Earths deep interior, H2O exists in the form of O-H groups in ultra-dense hydrous minerals, which have been proved to be stable even at the conditions of the core-mantle boundary (CMB). However, the superionic states of these hydrous minerals at high P-T have not been investigated. Using first-principles calculations, we found that pyrite structured FeO2Hx (0 <= x <= 1) and d-AlOOH, which have been proposed to be major hydrogen-bearing phases in the deep lower mantle (DLM), contain superionic hydrogen at high P-T conditions. Our observations indicate a universal pathway of the hydroxyl O-H at low pressure transforming to symmetrical O-H-O bonding at high-P low-T, and a superionic state at high-P high-T. The superionicity of hydrous minerals has a major impact on the electrical conductivity and hydrogen transportation behaviors of Earths lower mantle as well as the CMB.
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