China's Clear Spherical Neutrino Detector Hits Key Phase
China's transparent spherical neutrino detector has reached a pivotal milestone in its development.
TroibNews 
On Wednesday, China commenced the filling of the world's largest transparent spherical detector with ultrapure water, marking a significant milestone in the construction of the neutrino research facility.
The ultrapure water has undergone extensive filtration through various stages of a water purification system and is being injected into the detector pool of the Jiangmen Underground Neutrino Observatory at a rate of 100 tonnes per hour, as stated by the Institute of High Energy Physics under the Chinese Academy of Sciences, which is leading the project.
At the heart of the JUNO is a liquid scintillator detector located in a cylindrical pool that reaches a depth of 44 meters, situated within an underground hall buried deep within a granite hillside in Kaiping, Jiangmen City, Guangdong Province. This detector is encased in a stainless steel mesh shell with a diameter of 41.1 meters, which supports an acrylic sphere measuring 35.4 meters in diameter, designed to hold 20,000 tonnes of liquid scintillator.
The detector is outfitted with 20,000 photomultiplier tubes measuring 20 inches and an additional 25,000 tubes that are 3 inches in size, along with cables, magnetic shielding coils, light baffles, and other essential components.
The pool that houses the detector acts as both a water Cherenkov detector and a shield. At its top, it features a 1,000-square-meter cosmic ray tracker. Together, the water Cherenkov detector and cosmic ray tracker work to detect cosmic rays, mitigating their effects on neutrino detection.
Furthermore, the pool's water shields against natural radioactivity from the surrounding rock and secondary particles generated by cosmic rays impacting nearby rocks.
The photomultiplier tubes lining the inner walls of the liquid scintillator detector will collectively detect scintillation light produced when neutrinos interact with the liquid scintillator, converting the light signals into electrical signals for output.
In comparison to leading international standards, the volume of the liquid scintillator has expanded by 20 times, the photoelectron yield has tripled, and the energy resolution has reached an unprecedented 3 percent.
The filling process is planned in two phases. The first phase involves filling the pool and the interior of the acrylic sphere with ultrapure water over the next two months. Following that, the ultrapure water inside the acrylic sphere will be replaced with liquid scintillator over a period of six months.
Completion of the entire filling process is anticipated by August 2025, after which formal operations and data collection will begin.
Neutrinos are the smallest and lightest of the 12 elementary particles that constitute the material universe. Being electrically neutral, they travel at speeds nearly matching that of light. Since the Big Bang, neutrinos have been ubiquitous throughout the universe, influencing phenomena such as nuclear reactions in stars, supernova explosions, nuclear reactor operations, and radioactive decay in rocks.
Due to their minimal interaction with ordinary matter, neutrinos can pass through our bodies, buildings, and even the Earth with ease, earning them the moniker "ghost particles." Their elusive nature makes them the least understood of fundamental particles, necessitating the use of massive detectors to capture their faint traces.
The primary scientific objective of JUNO is to measure the neutrino mass hierarchy, with numerous other advanced research projects also planned. The JUNO team consists of over 700 members from 17 countries and regions.
JUNO is poised to become a significant center for international neutrino research, joining the ranks of the Hyper-Kamiokande neutrino experiment in Japan and the Deep Underground Neutrino Experiment in the United States, both of which are currently under construction.
Camille Lefevre for TROIB News
The ultrapure water has undergone extensive filtration through various stages of a water purification system and is being injected into the detector pool of the Jiangmen Underground Neutrino Observatory at a rate of 100 tonnes per hour, as stated by the Institute of High Energy Physics under the Chinese Academy of Sciences, which is leading the project.
At the heart of the JUNO is a liquid scintillator detector located in a cylindrical pool that reaches a depth of 44 meters, situated within an underground hall buried deep within a granite hillside in Kaiping, Jiangmen City, Guangdong Province. This detector is encased in a stainless steel mesh shell with a diameter of 41.1 meters, which supports an acrylic sphere measuring 35.4 meters in diameter, designed to hold 20,000 tonnes of liquid scintillator.
The detector is outfitted with 20,000 photomultiplier tubes measuring 20 inches and an additional 25,000 tubes that are 3 inches in size, along with cables, magnetic shielding coils, light baffles, and other essential components.
The pool that houses the detector acts as both a water Cherenkov detector and a shield. At its top, it features a 1,000-square-meter cosmic ray tracker. Together, the water Cherenkov detector and cosmic ray tracker work to detect cosmic rays, mitigating their effects on neutrino detection.
Furthermore, the pool's water shields against natural radioactivity from the surrounding rock and secondary particles generated by cosmic rays impacting nearby rocks.
The photomultiplier tubes lining the inner walls of the liquid scintillator detector will collectively detect scintillation light produced when neutrinos interact with the liquid scintillator, converting the light signals into electrical signals for output.
In comparison to leading international standards, the volume of the liquid scintillator has expanded by 20 times, the photoelectron yield has tripled, and the energy resolution has reached an unprecedented 3 percent.
The filling process is planned in two phases. The first phase involves filling the pool and the interior of the acrylic sphere with ultrapure water over the next two months. Following that, the ultrapure water inside the acrylic sphere will be replaced with liquid scintillator over a period of six months.
Completion of the entire filling process is anticipated by August 2025, after which formal operations and data collection will begin.
Neutrinos are the smallest and lightest of the 12 elementary particles that constitute the material universe. Being electrically neutral, they travel at speeds nearly matching that of light. Since the Big Bang, neutrinos have been ubiquitous throughout the universe, influencing phenomena such as nuclear reactions in stars, supernova explosions, nuclear reactor operations, and radioactive decay in rocks.
Due to their minimal interaction with ordinary matter, neutrinos can pass through our bodies, buildings, and even the Earth with ease, earning them the moniker "ghost particles." Their elusive nature makes them the least understood of fundamental particles, necessitating the use of massive detectors to capture their faint traces.
The primary scientific objective of JUNO is to measure the neutrino mass hierarchy, with numerous other advanced research projects also planned. The JUNO team consists of over 700 members from 17 countries and regions.
JUNO is poised to become a significant center for international neutrino research, joining the ranks of the Hyper-Kamiokande neutrino experiment in Japan and the Deep Underground Neutrino Experiment in the United States, both of which are currently under construction.
Camille Lefevre for TROIB News
