Partial radiogenic heat model for Earth revealed by geoneutrino measurements

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Abstract

The Earth has cooled since its formation, yet the decay of radiogenic isotopes, and in particular uranium, thorium and potassium, in the planet’s interior provides a continuing heat source. The current total heat flux from the Earth to space is 44.2±1.0 TW, but the relative contributions from residual primordial heat and radiogenic decay remain uncertain. However, radiogenic decay can be estimated from the flux of geoneutrinos, electrically neutral particles that are emitted during radioactive decay and can pass through the Earth virtually unaffected. Here we combine precise measurements of the geoneutrino flux from the Kamioka Liquid-Scintillator Antineutrino Detector, Japan, with existing measurements from the Borexino detector, Italy. We find that decay of uranium-238 and thorium-232 together contribute  TW to Earth’s heat flux. The neutrinos emitted from the decay of potassium-40 are below the limits of detection in our experiments, but are known to contribute 4 TW. Taken together, our observations indicate that heat from radioactive decay contributes about half of Earth’s total heat flux. We therefore conclude that Earth’s primordial heat supply has not yet been exhausted.

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Figure 1: Prompt energy spectrum and event selection efficiency.
Figure 2: Event-rate correlation.
Figure 3: CL of geoneutrino events.
Figure 4: Measured geoneutrino flux and models.

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Acknowledgements

We thank E. Ohtani and W. F. McDonough for advice and guidance. The KamLAND experiment is supported by a Grant-in-Aid for Specially Promoted Research under grant 16002002 of the Japanese Ministry of Education, Culture, Sports, Science and Technology; the World Premier International Research Center Initiative (WPI Initiative), MEXT, Japan; and the US Department of Energy (DOE) grants DEFG03-00ER41138 and DE-AC02-05CH11231, as well as other DOE grants to individual institutions. The reactor data are provided by courtesy of the following electric associations in Japan: Hokkaido, Tohoku, Tokyo, Hokuriku, Chubu, Kansai, Chugoku, Shikoku and Kyushu Electric Power Companies, Japan Atomic Power Company and Japan Atomic Energy Agency. The Kamioka Mining and Smelting Company has provided service for activities in the mine.

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All authors contributed equally to the work presented in this study.

Correspondence to I. Shimizu.

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The author declare no competing financial interests.

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Gando, A., Gando, Y., Ichimura, K. et al. Partial radiogenic heat model for Earth revealed by geoneutrino measurements. Nature Geosci 4, 647–651 (2011) doi:10.1038/ngeo1205

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