China’s Jiangmen Underground Neutrino Observatory (Juno) in Guangdong province has reached a significant milestone as it fills its massive detector with ultrapure water. This marks the final stage before the facility commences operations to study neutrinos, often called “ghost particles” due to their elusive nature.
The ultrapure water, crucial for detecting faint interactions caused by neutrinos, is being pumped into the detector at 100 tonnes per hour. According to the Institute of High Energy Physics (IHEP) of the Chinese Academy of Sciences, Juno will begin data collection by August next year.
At the heart of Juno lies a subterranean spherical detector designed to measure the mass of different neutrino types generated by nearby nuclear power plants. The sphere, which measures approximately 35 meters in diameter, will eventually be filled with 20,000 tonnes of liquid scintillator and immersed in 35,000 tonnes of pure water. Positioned 700 meters below ground, this setup minimizes interference from cosmic radiation, enabling more precise measurements.
The water-filling process will unfold in two phases over eight months. Initially, the interior and exterior of the sphere will be filled with ultrapure water over two months. In the next six months, a liquid scintillator will replace the water inside the sphere. This scintillator is key to detecting neutrinos, as rare interactions with the liquid will produce brief flashes of light captured by thousands of phototubes lining the detector.
Juno represents a significant advancement in neutrino research and is part of a global effort to unlock the mysteries of these fundamental particles. Similar large-scale neutrino observatories, including the Deep Underground Neutrino Experiment (DUNE) in the United States and Japan’s Hyper-Kamiokande project, are expected to become operational in the coming years.
The Juno project, with a budget of US$376 million, involves 750 researchers from 74 institutions across 17 countries, highlighting the international collaboration driving this initiative. Around 300 of these researchers hail from European nations such as Italy, Germany, and France.
Wang Yifang, director of the IHEP, emphasized that Juno’s completion will bolster China’s leadership in neutrino research and contribute to the broader scientific effort to understand better the fundamental forces shaping the universe.
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