Geoneutrinos & understanding Earth heat flux

Written by Journal of Physics on January 8, 2018. Posted in Current News

The paper identifies that thermal conduction does not include the heat of gases vented from within the planet. Correcting for the Enthalpy carried in these vented gases yields estimates of the planet’s internal heat ranging from 300 to 420 TW, nearly ten times the prevailing view.  Of course, the vast bulk such heat is dissipated into the ocean waters.

The body of ‘hot’ water in the western Pacific which drives the El Niño is centered directly over the Mariana Trench, only exceeded by the North Pole’s Gakkel Ridge as the closet points to the Earth’s great internal heat engine.

Abstract. 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.

1. Introduction
So far there are only two detectors, Borexino [1] and KamLAND [2], which reported registration of geoneutrino signals. Geoneutrinos are electron antineutrinos produced in beta-decays of radioactive elements in natural families of 238U, 232Th and 40K, accumulated inside the Earth. Geoneutrino flux on the Earth surface depends on the amounts of 238U, 232Th and 40K in the Earth and their distribution with the depth.

Amounts of 238U, 232Th and 40K in the Earth and their distribution are different in existing models of the Earth. The theory most popular at the moment is called the Bulk Silicate Earth (BSE) [3, 4]. Its main idea is that element abundances are the same as in meteorites. Based on this idea the amounts of 238U, 232Th and 40K were obtained for the Earth:

MBSE(238U) = 0,81∙1017 kg, MBSE(232Th) = 3,16∙1017 kg and MBSE(40K) = 5,73∙1016 kg. (1) These masses are distributed mainly in the Earth crust and partially in its mantle, but they are absent in its core. Experimentally observed antineutrino flux is in agreement with 238U and 232Th amounts from (1) under the assumption that they are distributed in the crust and in the upper mantle [1] only.

Each radioactive decay accompanied by a definite thermal energy emission. If we know the total amounts of 238U, 232Th and 40K in the Earth, the value of radiogenic heat flux can be predicted and it can be compared with experimentally measured one.

The Earth thermal flux on continents in boreholes is explored by the measurement of the temperature gradient at depths of ~500 meters. The thermal flux in oceans is measured by dedicated apparatus which penetrates to the bottom floor by several meters and measures the temperature gradient. To calculate the value of thermal flux one uses the idea that the main thermo-transfer mechanism is a thermal conductivity. Presently the value obtained from experimental measurements assuming the foregoing point of view is 47±2 TW.

The calculated inner Earth thermal flux appears to be equal to 17.5 TW. In this calculation the total masses of 238U, 232Th and 40K in the Earth were taken from (1). Comparison of this value with experimental one did not confirm correctness of the BSE basic assumptions. Researches started to look for additional heat sources.

In this paper we will use an alternative Earth model, so called the Hydride Earth model (HE) [5], and discuss how predictions of geoneutrino and thermal fluxes are correspond to the observed data.

Read more at: iopscience.iop.org

Authors:

L B Bezrukov, A S Kurlovich, B K Lubsandorzhiev, A K Mezhokh , V P Morgalyuk , V V Sinev1, and V P Zavarzina, Institute for Nuclear Researches of Russian Academy of Sciences, Prospekt 60-letia, Oktyabrya 7a, 115409 Moscow, Russia; A. N. Nesmeyanov Institute of Organoelement Compounds of Russian Academy of Sciences, Vavilova 10, 115409 Moscow, Russia

E-mail: [email protected]

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