How Geoneutrinos can help in understanding of the Earth heat flux

Written by L B Bezrukov, A S Kurlovich et al. on April 5, 2018. Posted in Current News

New study in the Journal of Physics, using a Hydide Earth model (HE) predicts production of gases at high depths. Considered factors were geoneutrino fluxes, temperature profiles of super deep boreholes and experimentally observed increase of the ocean temperature. [1]

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. [PSI Editor’s note:Besides Borexino and KAMLand, there are Baksan (Russia), Boulby (U.K.), Fairport Harbor (Ohio, U.S.), SNO+ (Ontario, Canada), JUNO & Jimping (China).]

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

Read more at iopscience.iop.org

[1] How Geoneutrinos can help in understanding of the Earth heat flux,  L B Bezrukov et al 2017 J. Phys.: Conf. Ser. 934 012011, http://iopscience.iop.org/article/10.1088/1742-6596/934/1/012011/pdf

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