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Experimental investigation of geologically produced antineutrinos with KamLAND


The detection of electron antineutrinos produced by natural radioactivity in the Earth could yield important geophysical information. The Kamioka liquid scintillator antineutrino detector (KamLAND) has the sensitivity to detect electron antineutrinos produced by the decay of 238U and 232Th within the Earth. Earth composition models suggest that the radiogenic power from these isotope decays is 16 TW, approximately half of the total measured heat dissipation rate from the Earth. Here we present results from a search for geoneutrinos with KamLAND. Assuming a Th/U mass concentration ratio of 3.9, the 90 per cent confidence interval for the total number of geoneutrinos detected is 4.5 to 54.2. This result is consistent with the central value of 19 predicted by geophysical models. Although our present data have limited statistical power, they nevertheless provide by direct means an upper limit (60 TW) for the radiogenic power of U and Th in the Earth, a quantity that is currently poorly constrained.

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Figure 1: The expected 238U, 232Th and 40K decay chain electron antineutrino energy distributions.
Figure 2: The expected total 238U and 232Th geoneutrino flux within a given distance from KamLAND22.
Figure 3: ν̄ e energy spectra in KamLAND.
Figure 4: Confidence intervals for the number of geoneutrinos detected.
Figure 5

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We thank E. Ohtani and N. Sleep for advice and guidance. The KamLAND experiment is supported by the COE program of the Japanese Ministry of Education, Culture, Sports, Science, and Technology, and by the United States Department of Energy. The reactor data were provided courtesy of the following associations in Japan: Hokkaido, Tohoku, Tokyo, Hokuriku, Chubu, Kansai, Chugoku, Shikoku and Kyushu Electric Power Companies, Japan Atomic Power Co. and Japan Nuclear Cycle Development Institute. Kamioka Mining and Smelting Company provided services for activity at the experimental site.

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Correspondence to S. Enomoto or N. Tolich.

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Araki, T., Enomoto, S., Furuno, K. et al. Experimental investigation of geologically produced antineutrinos with KamLAND. Nature 436, 499–503 (2005).

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