Partial radiogenic heat model for Earth revealed by geoneutrino measurements

Journal name:
Nature Geoscience
Volume:
4,
Pages:
647–651
Year published:
DOI:
doi:10.1038/ngeo1205
Received
Accepted
Published online

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±1.0TW, 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 4TW. 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.

At a glance

Figures

  1. Prompt energy spectrum and event selection efficiency.
    Figure 1: Prompt energy spectrum and event selection efficiency.

    a, Prompt energy spectrum of low-energy s in KamLAND. The histograms indicate the backgrounds, whereas the best fit (including geoneutrinos) is shown in blue. b, Background-subtracted energy spectrum. The blue shaded spectrum is the expectation from the reference model, consisting of contributions from U (dashed curve) and Th (dotted curve). c, Energy dependence of the geoneutrino event selection efficiency averaged over the data-taking period. Statistical uncertainties are shown for the data in a, and uncertainties on the background estimation are added in b.

  2. Event-rate correlation.
    Figure 2: Event-rate correlation.

    a, Expected and measured rates at KamLAND for s with energies between 0.9MeV and 2.6MeV. The points indicate the measured rates, whereas the curves show the expected rates for reactor s, reactor s +other backgrounds, and reactor s + backgrounds + geoneutrinos. The vertical bands correspond to data periods not used owing to high noise resulting from purification activities. b, Measured event rates plotted against the expected rate from reactor s + other backgrounds. The dotted line is the best linear fit. The shaded region is the ±1σ fit envelope. The error bars are statistical only.

  3. CL of geoneutrino events.
    Figure 3: CL of geoneutrino events.

    a, CL contours and best-fit point for the observed geoneutrino event rates. The small shaded region is favoured by the reference model4. The dashed line is the locus of points expected from the BSE model of ref. 5, Th:U=3.9. b,  Δχ2-profile from the fit to the total number of geoneutrino events discussed in the text. In this case the Th:U ratio is fixed at 3.9. The BSE model prediction is represented by the shaded band5.

  4. Measured geoneutrino flux and models.
    Figure 4: Measured geoneutrino flux and models.

    a, Measured geoneutrino flux at Kamioka and Gran Sasso, and expected fluxes at these sites and Hawaii4. The solid and dashed red lines represent, respectively, the fluxes for a fully radiogenic model assuming the homogeneous and sunken-layer hypotheses. b, Measured geoneutrino flux after subtracting the estimated crustal contribution. No modelling uncertainties are shown. The right axis shows the corresponding radiogenic heat production assuming a homogeneous mantle. The solid red line indicates the fully radiogenic model where the contributions from the crust (7.0TW) and the other isotopes6, 24 (4.3TW) are subtracted from the total heat flow7 (44.2TW). Error bars, see text.

References

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Author information

Affiliations

  1. Research Center for Neutrino Science, Tohoku University, Sendai 980-8578, Japan

    • The KamLAND Collaboration,
    • A. Gando,
    • Y. Gando,
    • K. Ichimura,
    • H. Ikeda,
    • K. Inoue,
    • Y. Kibe,
    • Y. Kishimoto,
    • M. Koga,
    • Y. Minekawa,
    • T. Mitsui,
    • T. Morikawa,
    • N. Nagai,
    • K. Nakajima,
    • K. Nakamura,
    • K. Narita,
    • I. Shimizu,
    • Y. Shimizu,
    • J. Shirai,
    • F. Suekane,
    • A. Suzuki,
    • H. Takahashi,
    • N. Takahashi,
    • Y. Takemoto,
    • K. Tamae,
    • H. Watanabe,
    • B. D. Xu,
    • H. Yabumoto,
    • H. Yoshida &
    • S. Yoshida
  2. Institute for the Physics and Mathematics of the Universe, Tokyo University, Kashiwa 277-8568, Japan

    • K. Inoue,
    • M. Koga,
    • K. Nakamura,
    • S. Enomoto,
    • A. Kozlov,
    • H. Murayama,
    • A. Piepke,
    • S. J. Freedman,
    • B. K. Fujikawa,
    • G. A. Horton-Smith,
    • Y. Efremenko,
    • K. M. Heeger &
    • M. P. Decowski
  3. Physics Department, University of California, Berkeley and Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA

    • H. Murayama,
    • T. I. Banks,
    • T. Bloxham,
    • J. A. Detwiler,
    • S. J. Freedman,
    • B. K. Fujikawa,
    • K. Han,
    • R. Kadel,
    • T. O’Donnell &
    • H. M. Steiner
  4. Department of Physics and Astronomy, University of Alabama, Tuscaloosa, Alabama 35487, USA

    • C. Grant,
    • G. Keefer &
    • A. Piepke
  5. W. K. Kellogg Radiation Laboratory, California Institute of Technology, Pasadena, California 91125, USA

    • D. A. Dwyer,
    • R. D. McKeown &
    • C. Zhang
  6. Department of Physics, Colorado State University, Fort Collins, Colorado 80523, USA

    • B. E. Berger
  7. Physics Department, Drexel University, Philadelphia, Pennsylvania 19104, USA

    • C. E. Lane,
    • J. Maricic &
    • T. Miletic
  8. Department of Physics and Astronomy, University of Hawaii at Manoa, Honolulu, Hawaii 96822, USA

    • M. Batygov,
    • J. G. Learned,
    • S. Matsuno &
    • M. Sakai
  9. Department of Physics, Kansas State University, Manhattan, Kansas 66506, USA

    • G. A. Horton-Smith
  10. Physics Department, Stanford University, Stanford, California 94305, USA

    • K. E. Downum,
    • G. Gratta &
    • K. Tolich
  11. Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996, USA

    • Y. Efremenko &
    • O. Perevozchikov
  12. Triangle Universities Nuclear Laboratory, Durham, North Carolina 27708, USA

    • H. J. Karwowski,
    • D. M. Markoff &
    • W. Tornow
  13. Physics Departments at Duke University, North Carolina Central University, and the University of North Carolina at Chapel Hill, USA

    • H. J. Karwowski,
    • D. M. Markoff &
    • W. Tornow
  14. Department of Physics, University of Wisconsin, Madison, Wisconsin 53706, USA

    • K. M. Heeger
  15. Nikhef, Science Park 105, 1098 XG Amsterdam, The Netherlands

    • M. P. Decowski

Consortia

  1. The KamLAND Collaboration

    • A. Gando,
    • Y. Gando,
    • K. Ichimura,
    • H. Ikeda,
    • K. Inoue,
    • Y. Kibe,
    • Y. Kishimoto,
    • M. Koga,
    • Y. Minekawa,
    • T. Mitsui,
    • T. Morikawa,
    • N. Nagai,
    • K. Nakajima,
    • K. Nakamura,
    • K. Narita,
    • I. Shimizu,
    • Y. Shimizu,
    • J. Shirai,
    • F. Suekane,
    • A. Suzuki,
    • H. Takahashi,
    • N. Takahashi,
    • Y. Takemoto,
    • K. Tamae,
    • H. Watanabe,
    • B. D. Xu,
    • H. Yabumoto,
    • H. Yoshida,
    • S. Yoshida,
    • S. Enomoto,
    • A. Kozlov,
    • H. Murayama,
    • C. Grant,
    • G. Keefer,
    • A. Piepke,
    • T. I. Banks,
    • T. Bloxham,
    • J. A. Detwiler,
    • S. J. Freedman,
    • B. K. Fujikawa,
    • K. Han,
    • R. Kadel,
    • T. O’Donnell,
    • H. M. Steiner,
    • D. A. Dwyer,
    • R. D. McKeown,
    • C. Zhang,
    • B. E. Berger,
    • C. E. Lane,
    • J. Maricic,
    • T. Miletic,
    • M. Batygov,
    • J. G. Learned,
    • S. Matsuno,
    • M. Sakai,
    • G. A. Horton-Smith,
    • K. E. Downum,
    • G. Gratta,
    • K. Tolich,
    • Y. Efremenko,
    • O. Perevozchikov,
    • H. J. Karwowski,
    • D. M. Markoff,
    • W. Tornow,
    • K. M. Heeger &
    • M. P. Decowski

Contributions

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

Competing financial interests

The authors declare no competing financial interests.

Corresponding author

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