There are a lot of neutrinos in our immediate neighborhood. It is estimated that about 60 billion of them pass through every square centimeter of the Earth’s surface every second. These particles come from really cool places in the universe. Some of them form directly in the center of the Sun, others reach the Earth created in supernova explosions, in the centers of active galactic nuclei, and some may also in the Big Bang. Because they are reluctant to interact with interstellar matter, neutrinos released in a distant explosion often reach Earth first, followed by light.
However, it should be noted that we also have locally generated neutrinos, the source of which is, for example, the decay of radioactive elements underground, nuclear reactors and, finally, particle accelerators. Suffice it to mention here the neutrinos that originated in the Large Hadron Collider and were recorded by one of the side experiments.
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When studying neutrinos, physicists and astronomers primarily want to discover where they come from and the processes through which they are created. After all, if neutrinos were created inside a star, such as the sun, they are in fact the only direct witnesses to what is happening inside the sun. No other particle can tell us that directly.
Observing neutrinos is a huge challenge
Because neutrinos interact roughly with matter, they can travel thousands of light-years without being disturbed by interstellar gas or dust. Moreover, when a neutrino hits the Earth, it flies right through it and keeps going. However, when some interaction occurs, nothing happens to the particle itself, but such an encounter leaves behind new interactions or particles that can already be detected. A good example of this is, for example, the capture of neutrinos by tetrachlorethylene, an agent commonly used in dry cleaning. When a neutrino hits a chlorine-37 atom in a tank filled with this compound, it turns it into an argon-37 atom, and this change can only be noticed by detectors.
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Due to the fact that this happens extremely rarely, despite the fact that there are a lot of neutrinos flying around the Earth, you still need a powerful detector with a large surface area to record at least a few of them.
Here you can select an alternative method to search for neutrinos. Huge tanks filled with water, heavy water or ice. When a charged particle like a neutrino passes through this detector, it generates a special kind of radiation, called Cherenkov radiation. So it is enough to build a large tank of this type, put thousands of radiation detectors around it, and you can wait for neutrinos. The problem is that this detector must be separated from other types of local radiation. For this reason, Cherenkov radiation detectors are built deep in the ground or, for example, at the bottom of deep water tanks. No wonder the largest detectors on Earth are located in Antarctica (IceCube), at the bottom of Lake Baikal, and finally at the bottom of the Mediterranean Sea.
China is building a giant new neutrino detector
A team of Chinese scientists plans to build The world’s largest neutrino detector to date. According to representatives of the Chinese Academy of Sciences, this is a 30-square-kilometer detector with more than 55,000 optical sensors strung on more than two thousand wires. The main task of the new observatory will be to detect high-energy neutrinos that could be directly related to cosmic rays, that is, energetic particles that constantly bombard the Earth. Scientists believe that neutrinos, cosmic rays, and gamma rays may have a common origin. However, to confirm this, it is necessary to record all these particles that reach us at the same time from the same source. The new detector has a chance to do so as soon as it goes into service. However, we still have to wait for that a bit. Currently, the first tests of the detector are taking place at a depth of more than 1,800 meters below the surface of the water.
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