China has begun filling the world’s largest transparent spherical neutrino detector with ultrapure water, marking a significant milestone in the construction of the Jiangmen Underground Neutrino Observatory (JUNO).
On Wednesday, the Institute of High Energy Physics under the Chinese Academy of Sciences announced that ultrapure water is being injected into the detector pool at a flow rate of 100 tonnes per hour. This process signifies that JUNO has reached its last critical stage before becoming fully operational.
Located deep underground in Kaiping, Jiangmen City, Guangdong Province, the core of JUNO is a liquid scintillator detector immersed in a 44-meter-deep cylindrical pool. The detector is supported by a 41.1-meter-diameter stainless steel mesh shell, which holds a 35.4-meter-diameter acrylic sphere designed to be filled with 20,000 tonnes of liquid scintillator.
The detector is equipped with 20,000 large 20-inch photomultiplier tubes and 25,000 smaller 3-inch photomultiplier tubes, along with cables, magnetic shielding coils, and light baffles. These components work in unison to detect the faint light signals produced when neutrinos interact with the liquid scintillator, converting them into electrical signals for analysis.
A water Cherenkov detector and a cosmic ray tracker are integrated into the pool housing the detector. Together, they detect cosmic rays and shield the detector from natural radioactivity and other interferences from the surrounding environment, ensuring the purity and accuracy of the neutrino measurements.
Compared to previous detectors, JUNO boasts a liquid scintillator volume 20 times larger, a photoelectron yield three times higher, and an unprecedented energy resolution of 3 percent. These advancements position JUNO at the forefront of neutrino research globally.
The filling process is conducted in two phases. In the first two months, the pool and the space inside the acrylic sphere will be filled with ultrapure water. Subsequently, over six months, the water inside the acrylic sphere will be gradually replaced with the liquid scintillator. The entire process is expected to be completed by August 2025, after which JUNO will begin formal operation and data collection.
Neutrinos are electrically neutral, nearly massless particles that travel at speeds close to light. They are abundant in the universe but interact very weakly with matter, making them challenging to detect. JUNO aims to measure the neutrino mass hierarchy as its primary scientific goal, which could unlock many mysteries about the fundamental properties of matter and the universe.
The JUNO collaboration includes over 700 scientists from 17 countries and regions, highlighting the international significance of this project. Once operational, JUNO will stand alongside other major neutrino research facilities under construction, such as the Hyper-Kamiokande experiment in Japan and the Deep Underground Neutrino Experiment in the United States.
This milestone in China’s scientific endeavor not only demonstrates the nation’s growing capabilities in fundamental research but also contributes significantly to the global scientific community’s understanding of the universe.
Reference(s):
China's transparent spherical neutrino detector reaches critical stage
cgtn.com
