China built a 'ghost particle' detector at a depth of 700m

The Jiangmen Underground Neutrino Observatory is under construction.

The main structure consists of a giant spherical stainless steel mesh that will support JUNO's core device - a spherical detector as tall as a 13-story building, covered by 20,000 photomultiplier tubes that detect light and filled with 20,000 tons of specially formulated liquid.

The entire structure was built in the center of a water tank located under a large cave in Jiangmen city. Engineers will use a lifting platform to install the acrylic sphere from top to bottom inside the wire mesh. At the same time, photomultiplier tubes and other components will also be attached to the wire mesh. Once complete, the acrylic sphere will be filled with a flickering liquid, while a water bath will cover the entire detector to protect it from the natural radiation of the surrounding rocks.

Neutrinos, also known as "ghost particles", are elementary particles with so little mass that they were once thought to be massless. It is the second most abundant particle in the universe after light particles (photons).

As the neutrinos pass through the detector, a very small fraction of them will interact with the liquid, creating a flickering light that is detected by the photomultiplier tubes as a neutrino signal for further calculation and study. Besides neutrinos from nuclear reactors, JUNO can also study neutrinos from supernovas, the Sun, Earth and our atmosphere.

The JUNO Observatory is operated by the Institute of High Energy Physics of the Chinese Academy of Sciences. Its power comes from the Yangjiang and Taishan nuclear power plants, both more than 50km away.

The $305.3 million ghost particle detector is expected to be completed and put into use in 2023, making it the second-largest neutrino experiment facility in China. It is designed to detect and measure the quality of neutrinos with unprecedented precision and resolution, helping scientists better understand their mass, how they can change identity between in the process of oscillation and solve many mysteries about this elementary but very elusive particle.