JUNO for Jiangmen Underground Neutrino Observatory. This is the name given to an enormous sphere 44 meters deep located 700 meters underground in China. Equipped with thousands of tubes capable of detecting light, it will be placed in a cylindrical water tank approximately 35 meters in diameter.
But what is it and what will it be used for? It is an observatory whose objective is to unravel the mysteries of neutrino oscillations, these particles constantly change “type” during their movement. Since the mid-1940s, when they were discovered, these particles have intrigued scientists, and several laboratories, including French, are participating in this international project. It's very simple, we consider neutrinos to be “one of the greatest mysteries of particle physics” and we nickname them “ghost particles”.
They pass through our body without leaving any traces!
As neutrinos are produced in abundance by nuclear reactions, the location of this sphere is strategic: it is positioned between two Chinese nuclear power plants. Over a period of 6 years, researchers will be able to observe a large number of neutrinos and thus refine their measurements.
But the real difficulty lies in the fact that these particles rarely interact with matter. Every second, billions of neutrinos pass through the Earth and therefore our bodies without leaving a trace. Even with this huge detector, only around forty interactions per day are expected.
20,000 tons of sparkling liquid
JUNO was built underground to isolate observations from background noise, such as cosmic rays. Thus, the 700 meters of rock above the observatory serve as a natural shield against these parasitic particles. The detector itself consists of several layers: there is this enormous metal sphere several tens of meters deep, in which we find another transparent acrylic glass sphere 35.4 meters in diameter.
The latter will be filled with 20,000 tons of sparkling liquid. This compound produces a light flash when a neutrino interacts with a proton in the liquid. These rare flashes will then be captured by photomultipliers, sensitive devices arranged around the sphere.
The United States is falling behind
In addition to monitoring neutrinos produced by power plants, JUNO will be able to detect other phenomena such as geoneutrinos, resulting from the radioactive decay of elements present in the earth's crust, or neutrinos originating from supernovae, extremely powerful stellar explosions. . These events will allow researchers to better understand the internal composition of the Earth as well as the mechanisms that govern these cosmic explosions.
If JUNO should be operational in the second half of 2025, a similar project led by the United States has fallen behind schedule. This is DUNE, whose costs have exploded: three billion dollars, ten times more than the cost of the Chinese laboratory.
As in the conquest of space, China has caught up, and even taken a lead in certain areas.
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