China has turned on the world's most sensitive neutrino detector after more than a decade of construction. The Register reports:

> The Jiangmen Underground Neutrino Experiment (JUNO) is buried 700 meters under a mountain and features a 20,000-tonne "liquid scintillator detector" that China's Academy of Science [1]says is "housed at the center of a 44-meter-deep water pool." There's also a 35.4-meter-diameter acrylic sphere supported by a 41.1-meter-diameter stainless steel truss. All that stuff is surrounded by more than 45,000 photo-multiplier tubes (PMTs). The latter devices are super-sensitive light detectors. A liquid scintillator is a fluid that, when exposed to ionizing radiation, produces light. At JUNO, the liquid is 99.7 percent alkylbenzene, an ingredient found in detergents and refrigerants.

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> JUNO's designers hope that any neutrinos that pass through its giant tank bonk a hydrogen atom and produce just enough light that the detector array of PMTs can record their passing, producing data scientists can use to learn more about the particles. At this point, readers could sensibly ask how JUNO will catch any of these elusive particles. The answer lies in the facility's location -- a few tens of kilometers away from two nuclear power plants that produce neutrinos.

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> The Chinese Academy of Science's Journal of High Energy Physics [2]says trials of JUNO succeeded, suggesting it will be able to help scientists understand why some neutrinos are heavier than others so we can begin to classify the different types of the particle -- a key goal for the facility. The Journal also reports that scientists from Japan, the United States, Europe, India, and South Korea, are either already using JUNO or plan experiments at the facility.



[1] https://english.cas.cn/newsroom/cas_media/202508/t20250827_1051466.shtml

[2] https://ihep.cas.cn/dkxzz/juno/JUNO_dongtai/202508/t20250827_7915624.html