In the 1990s, Japan spent a huge amount of money to build a cylindrical stainless steel container with a height of 41.4 meters and a diameter of 39.3 meters in depth in the Shigeju Mine, Kamiocho, Hida City, Gifu Prefecture. The inner wall of this container was densely packed with golden spheres.
This cylindrical stainless steel container is called Super Shengang Detector . It stores 50,000 tons of ultrapure water, which is about the amount of water in 20 standard swimming pools.
Why does Japan spend so much effort to store so much ultrapure water underground? What is its purpose?
Neutrino is a type of lepton . It is one of the most basic particles that make up nature and is usually represented by the symbol Greek letter ν. Neutrinos have neither positive charges of nor negative charges, so their properties are neutral. It took the scientific community more than 20 years from predicting the existence of neutrinos to discovering it.
Research shows that when nuclear fusion is performed inside the sun, a large number of neutrinos will be generated, some of which will fly to the earth.
Neutrinos are called "the most elusive prey in the universe". They have stumped many physics experts. Even the founder of quantum mechanics , Boer , almost gave up 's law of conservation of energy for it.
Since it does not carry any charge, neutrinos will not interact with matter. We can give an example. When the light from a flashlight shines on the wall, the light will be blocked by the wall. When the neutrinos shoot over, the wall will be penetrated directly as if it does not exist. In fact, not just walls, but the entire earth will be directly penetrated by neutrinos. Physicists speculate that about 1 million neutrinos pass through human bodies every second.
neutrinos are extremely small and cannot be seen at all by the naked eye. Even the smallest unit that makes up atom quark is two orders of magnitude larger than it.
The velocity of neutrinos in the vacuum is close to the speed of light, and its volume is almost negligible, so neutrinos are difficult to detect. However, some physicists have found through research that neutrinos will have different situations when they encounter water.
First, the velocity of neutrinos in water will not decrease, and it is well known that the velocity of light in water will decrease by about a quarter. Secondly, when neutrinos pass through the water, they may react with the water. Although the probability is small, it is also a breakthrough. Finally, neutrinos will emit Cherenkov radiation light when they enter the water.
Ultrapure water plays a very important role in this link. It not only helps scientists better discover the reactions of neutrinos in water, but also blocks the interference caused by other cosmic rays to the experiment.
The water we usually come into contact with contains impurities, whether it is tap water, mineral water or distilled water, without exception. Spring water contains a large amount of minerals, and tap water contains impurities such as silt, rust, algae, , suspended matter and microfiber. Usually we believe that the purest distilled water also contains a very small amount of impurities.
. Ultrapure water, also known as UP water, refers to water with a resistivity of 18 MΩ*cm (25℃). Apart from water molecules, there are almost no impurities in this water, nor do bacteria, viruses, chlorodioxin and other organic matter. Of course, there is no trace mineral elements needed by the human body, that is, water that almost removes all atoms except oxygen and hydrogen.
The 50,000 tons of ultrapure water stored in the Japanese Super Kaguoka Neutrino Detector is to capture neutrinos and use it to conduct a series of scientific experiments.
In order to maintain the purity of ultrapure water, the ultrapure water in these detectors has been in circulation and purification, striving to do everything possible to clean up trace impurities in it.
However, even though ultrapure water has reached 99.999% purity, it is still difficult to capture neutrinos because the radiation is too small. To this end, scientists need to use an instrument that can amplify radiation signals, which is the photomultiplier tube . The dense golden spheres on the inner wall of the Super Kanoka detector are actually photomultiplier tubes, which can amplify the signal of Cherenkov's radiated light by 100 million times.In this way, even the light that is so weak that it can be ignored can be captured.
In addition, in order to block out all other interference information as much as possible, the neutrino experiment needs high mountains as the background. However, Japan is an island country, and there is no mountain suitable for experiments in China, so they placed the experiment site in a waste mine 1,000 meters deep underground, so that the purpose of blocking interference signals can also be achieved.
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1996, after the Super Kaguoka detector was officially put into use, Japanese scientists quickly detected traces of neutrinos, confirmed the theory of supernova explosion , and kicked off the prelude to neutrino astronomy. The experimental results around neutrino research also brought two Nobel Prizes to Japan. The application prospects of
neutrinos are promising. Scientists can use the characteristics that neutrinos will not decay during the propagation process to calculate the real material content of each galaxy.
In addition, scientists can use the properties of neutrinos that can penetrate matter and can also apply it to the field of communications. In 2012, American scientists passed a neutrino through a rock as thick as 237 meters and transmitted the information it carried to a receiver on the back of the rock.
