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キーワード:
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要旨:
Nuclear reactors are strong and pure sources of electron-antineutrinos with energies up to about 10 MeV. Neutrino detectors positioned at different distances to the reactor core allow to investigate several of the most relevant parameters to describe the neutrino oscillation phenomenon.
In recent years, experiments at baselines of 1-2 km, such as Double Chooz, were able to measure the neutrino mixing angle θ13 with high precision. This fundamental parameter is highly relevant for future projects aiming to measure CP violation in the leptonic sector. At very short baselines, at the order of only 10 m, several projects, like Stereo, were searching for oscillations involving sterile neutrino states. The Stereo results disfavor the sterile neutrino hypothesis as a solution to the observed neutrino rate deficit as compared to predictions. The classical detection method in all these experiments is the inverse beta decay on hydrogen nuclei in organic scintillators. The larger cross section in coherent elastic neutrino nucleus scattering offers the possibility to detect the neutrino flux with much more compact detectors. Due to the higher interaction rate, the target mass can be reduced from the ton to the kg scale. This approach is currently studied in the CONUS experiment using high purity germanium detectors of very low energy threshold.
The requirements on the liquid scintillators used in Double Chooz and Stereo in terms of transparency, stability and safety were demanding. In particular, new solutions for the gadolinium loading had to be developed to assure that the detector specifications are met. Those included a light yield of more than 6000 photons/MeV and an attenuation length above 4m over a data taking period of about 5 years. New scintillator developments based on opaque, gel-like and safe materials might find applications in the upcoming generation of detectors. The progress in the technologies of organic scintillators as well as in the detection of the coherent scattering channel could enable the use of neutrino detectors for reactor monitoring and safeguard applications in the future.
