A "giant watermelon" hidden 700 meters underground? Go to the mysterious laboratory to search for "ghost particles" experiment | equipment | particles
In the deep mountains of Jiangmen, Guangdong, the large-scale scientific facility - Jiangmen Neutrino Experimental Facility - is under intense construction. This laboratory, hidden 700 meters underground, is studying a type of "ghost particle" in the universe - neutrinos.
What does this mysterious laboratory look like? Why did it have to be built so deep? What is "ghost particle"? CCTV News "Top Laboratory" takes you to explore the truth ↓
Going 700 meters underground
How difficult is it to capture "ghost particles"
Neutrinos are one of the smallest units that make up the material world, with a very ancient history. They were born a few seconds after the cosmic explosion.
Neutrinos are ubiquitous in the universe. Every second, 70 billion neutrinos pass through our fingertips. However, capturing it is not an easy task. Neutrinos are small, uncharged, and come and go without a trace. They can easily penetrate the human body and Earth, and are called "ghost particles".
The Jiangmen Neutrino Laboratory is a large-scale scientific facility built by the country to study neutrinos. By studying it, we may discover the secrets of the birth of the universe.
Why was it built in Jiangmen?
A nuclear reactor is the location on Earth where neutrinos are most concentrated. Jiangmen City is 53 kilometers away from both Yangjiang and Taishan nuclear power plants. After the completion of the two major reactors, their total power ranks first in the world and can obtain double the number of experimental samples.
It can be said that this is currently the most suitable place in the world for conducting neutrino experiments.
The laboratory is located 700 meters away from the top of the mountain directly above it. If the "Little Man Waist" of Guangzhou's new TV tower is placed underground, the top of the tower is still 100 meters away from the surface of the mountain.
Why build so deep? Due to strong cosmic rays on the ground, they can interfere with the detection of neutrinos. A 700 meter mountain and rock layer act as filters, greatly reducing the intensity of cosmic rays and allowing us to obtain pure neutrino signals.
It's not easy to go 700 meters deep underground, you need to take a "small train" and travel along the 1300 meter inclined shaft tunnel for nearly 20 minutes, just like a "geocentric adventure" ↓
Set multiple world records
What does this mysterious laboratory look like
Unlike typical laboratories, the main body of the Jiangmen neutrino experimental setup is like a watermelon soaked in ice water.
△ Jiangmen Neutrino Experimental Device
The outermost part is a grid structure composed of low radioactive stainless steel, which is the largest single stainless steel structure in China. The entire structure is fixed by 120000 sets of high-strength bolts.
The interior of the grid is the world's largest single organic glass structure - an organic glass ball with a diameter of 35.4 meters and a thickness of only 120 millimeters. Although as thin as an eggshell, it has extremely strong durability. The researchers used a body bonding process to make 263 glass panels seamlessly integrated, with no visible traces of splicing.
Organic glass balls under construction
The entire sphere constitutes the world's highest energy accuracy and largest liquid scintillator detector. However, to capture the figure of neutrinos, a key component is needed ↓
How to measure "ghost particles"
45000 "golden eyes" are the key
The most difficult hurdle in the development of the Jiangmen neutrino detector is the 45000 photomultiplier tubes, known as the most sensitive "detector eyes". These elliptical "golden pupils" can convert the light signals of neutrinos into electrical signals, amplify them by 10 million times, and obtain their energy, position, and other information, which are then analyzed and processed by computers.
△ photomultiplier tube
Before 2016, only one foreign company could produce 20 inch photomultiplier tubes, with prices generally ranging from 50000 to 60000 yuan per unit, resulting in extremely high procurement costs. At that time, achieving the localization of photomultiplier tubes was like a high mountain in front of scientific researchers.
Finally, after the painstaking research of Chinese researchers, in 2020, all 15000 photomultiplier tubes were manufactured and passed the acceptance inspection, achieving the localization of this technology and breaking the monopoly of more than 30 years abroad.
Now, the Jiangmen Neutrino Laboratory has been built for 10 years, and scientists, engineers, construction workers, and logistics personnel are doing what may be tedious but extremely romantic work - standing 700 meters underground, gazing up at the vast starry sky.
By next year, the organic glass ball in the experimental device center will be filled with liquid scintillators, and there will be no more human involvement in the next 20-30 years. It's like a match in the dark, waiting quietly for neutrinos to light up.
What kind of cosmic mysteries can be discovered here
Let's look forward to it together!
Producer | Liu Xin Xi Luo Xi
Producer | Ding Yi and Zhang Xian
Editor in Chief | Wu Tao
Director Yang Weixi, Pan Guohua, Sun Junwei
Camera Guide | Zhang Chunhu
Technical Support | Dong Xinwen, Hu Xinmei, Xia Xinyue, Song Jiamiao, Zhang Baiao, Zhang Luqi, Xu Yiguang
Visual | Yang Lu
Material support Liu Yuexiang, Institute of High Energy Physics, Chinese Academy of Sciences
Special thanks to Institute of High Energy Physics, Chinese Academy of Sciences
