11:00 〜 13:00
[SIT19-P08] 国内原子炉停止期間でのKamLANDによる地球ニュートリノ精密観測結果の報告
キーワード：地球ニュートリノ、地球進化、地球深部放射性物質
The decay of radioactive isotopes in the Earth is an important heat source, which drives the evolution of the Earth, and is crucial for understanding the history and dynamics of the Earth.
The amount of radioactive isotopes such as U, Th, and K can be measured by observing neutrinos emitted by decays of these isotopes (geo neutrinos).
KamLAND, an anti-electron neutrino detector located in Kamioka, Gifu Prefecture, was the first in the world to successfully observe neutrinos emitted from U and Th in the Earth in 2005.
KamLAND is an anti-electron neutrino detector consisting of about ~1 kt liquid scintillator and 1879 photomultiplier tubes. Anti-electron neutrinos is detected via the inverse-beta decay reaction between hydrogen nuclei in the liquid scintillator and anti-electron neutrinos. The delayed coincidence method of two spatially and temporally correlated events can significantly reduce the number of non-neutrino background events.
KamLAND was originally designed to verify neutrino oscillations through the observation of reactor neutrinos with energies of several MeV, and has succeeded in observing reactor neutrino oscillations over three cycles. On the other hand, reactor neutrinos are one of dominant backgrounds in the observation of geo neutrinos. However, the shutdown of commercial nuclear reactors in Japan due to the Great East Japan Earthquake in 2011 gave us an opportunity to precisely observe the earth neutrinos in an environment with few reactor neutrinos. In particular, the structure of the Earth's neutrino spectrum can now be seen, and it is now possible to measure the amounts of uranium and thorium in the Earth's interior independently. This means that not only can we directly verify the heat budget of the Earth, but we can also directly measure the chemical composition of the Earth's interior for the first time.
Independent measurements of U and Th abundances in the Earth using the reactor shutdown period confirmed that the abundance ratios of U and Th in the Earth's interior are consistent with the estimates from the BSE model. Assuming the U/Th abundance ratio and K abundance estimated from geoscience, the heat generated from radioactive isotopes in the Earth's interior is estimated to be about 14.8 TW.
Assuming a uniform distribution of radioactive materials in the mantle, the Fully-radiogenic model, which assumes that all the heat flow of about 47 TW currently visible on the earth's surface is due to radioactive isotopes, can be rejected with a confidence level of more than 99.99%. The High-Q model, which estimates more than 25 TW of radiogenic heat as the heat source driving mantle convection, is also rejected with a confidence level of 99.67%.
In this talk, I will report the results of about 20 years of earth neutrino observations by KamLAND.
The amount of radioactive isotopes such as U, Th, and K can be measured by observing neutrinos emitted by decays of these isotopes (geo neutrinos).
KamLAND, an anti-electron neutrino detector located in Kamioka, Gifu Prefecture, was the first in the world to successfully observe neutrinos emitted from U and Th in the Earth in 2005.
KamLAND is an anti-electron neutrino detector consisting of about ~1 kt liquid scintillator and 1879 photomultiplier tubes. Anti-electron neutrinos is detected via the inverse-beta decay reaction between hydrogen nuclei in the liquid scintillator and anti-electron neutrinos. The delayed coincidence method of two spatially and temporally correlated events can significantly reduce the number of non-neutrino background events.
KamLAND was originally designed to verify neutrino oscillations through the observation of reactor neutrinos with energies of several MeV, and has succeeded in observing reactor neutrino oscillations over three cycles. On the other hand, reactor neutrinos are one of dominant backgrounds in the observation of geo neutrinos. However, the shutdown of commercial nuclear reactors in Japan due to the Great East Japan Earthquake in 2011 gave us an opportunity to precisely observe the earth neutrinos in an environment with few reactor neutrinos. In particular, the structure of the Earth's neutrino spectrum can now be seen, and it is now possible to measure the amounts of uranium and thorium in the Earth's interior independently. This means that not only can we directly verify the heat budget of the Earth, but we can also directly measure the chemical composition of the Earth's interior for the first time.
Independent measurements of U and Th abundances in the Earth using the reactor shutdown period confirmed that the abundance ratios of U and Th in the Earth's interior are consistent with the estimates from the BSE model. Assuming the U/Th abundance ratio and K abundance estimated from geoscience, the heat generated from radioactive isotopes in the Earth's interior is estimated to be about 14.8 TW.
Assuming a uniform distribution of radioactive materials in the mantle, the Fully-radiogenic model, which assumes that all the heat flow of about 47 TW currently visible on the earth's surface is due to radioactive isotopes, can be rejected with a confidence level of more than 99.99%. The High-Q model, which estimates more than 25 TW of radiogenic heat as the heat source driving mantle convection, is also rejected with a confidence level of 99.67%.
In this talk, I will report the results of about 20 years of earth neutrino observations by KamLAND.