Antineutrino science by KamLAND.
Bottom Line:
KamLAND measured the ν̄ e's flux from distant nuclear reactors, and found fewer events than expected from standard assumptions about ν̄ e propagation at the 99.998% confidence level (C.L.).The total observed number of 4.5 to 54.2, assuming a Th/U mass concentration ratio of 3.9 is consistent with 19 predicted by geophysical models.This detection allows better estimation of the abundances and distributions of radioactive elements in the Earth, and of the Earth's overall heat budget.
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Affiliation: Director General, High Energy Accelerator Research Organization, Ibaraki, Japan . ; Director General, High Energy Accelerator Research Organization, Ibaraki, Japan .
ABSTRACT
KamLAND measured the ν̄ e's flux from distant nuclear reactors, and found fewer events than expected from standard assumptions about ν̄ e propagation at the 99.998% confidence level (C.L.). The observed energy spectrum disagrees with the expected spectral shape at 99.6% C.L., and prefers the distortion from neutrino oscillation effects. A two-flavor oscillation analysis of the data from KamLAND and solar neutrino experiments with CPT invariance, yields [Formula: see text] eV(2) and [Formula: see text]. All solutions to the solar neutrino problem except for the large mixing angle (LMA) region are excluded. KamLAND succeeded in detecting geoneutrinos produced by the decays of (238)U and (232)Th within the Earth. The total observed number of 4.5 to 54.2, assuming a Th/U mass concentration ratio of 3.9 is consistent with 19 predicted by geophysical models. This detection allows better estimation of the abundances and distributions of radioactive elements in the Earth, and of the Earth's overall heat budget. No MeSH data available. Related in: MedlinePlus |
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Mentions: To determine the reactor ν̄e flux, the information of instantaneous thermal power, fuel burn-up, exchange and enrichment records for all Japanese power reactors is required. The fission rate for each fissile element is calculated, combining all above data. The thermal power generation is checked with the independent records of electric power generation. Figs. 2 (a) and 2 (b) show one example of thermal power data and the corresponding fission-rate calculations for fissile elements of 235,238U and 239,241Pu of which elements contribute to 99.9% of the ν̄e flux generation. The time-integrated fission flux at Kamioka given by these fuel elements in units of fission number/cm2 is plotted in Fig. 2 (c) as a function of the distance. More than 79% of the total fission flux arises from 26 reactors within the distance of ∼180 km from Kamioka. This relatively narrow band of distances allows KamLAND to be sensitive to spectral distortions for certain oscillation parameters. The contribution to the ν̄e flux from Korean reactors is estimated to be (2.46 ± 0.25)% based on the reported electric power generation rates. That from other reactors around the world is (0.70± 0.35)% as an average. Once the fission rates of fissile isotopes are obtained, the expected ν̄e flux is calculated using the measurements of ν̄e energy spectrum per fission.4) |
View Article: PubMed Central - PubMed
Affiliation: Director General, High Energy Accelerator Research Organization, Ibaraki, Japan . ; Director General, High Energy Accelerator Research Organization, Ibaraki, Japan .
No MeSH data available.