Hidden at a depth of 1 km under Mount Ikeno, in the Kamioka zinc mine, 290 km north of Tokyo (Japan), there is a place that any supervillain from any movie or a superhero story would dream of as his lair. Here is the "Super-Kamiokande" (or "Super-K") - a neutrino detector. Neutrinos are subatomic fundamental particles that interact very weakly with ordinary matter. They are able to penetrate absolutely everything and everywhere. Observing these fundamental particles helps scientists find collapsing stars and learn new information about our universe. Business Insider spoke with three employees of the Super-Kamiokande station and found out how everything works here and what experiments scientists are conducting here.
Plunging into a subatomic world
Neutrinos are very difficult to detect. So difficult that the famous American astrophysicist and popularizer of science Neil DeGrasse Tyson once called them "the most elusive prey in space."
“Matter does not represent any obstacle for neutrinos. These subatomic particles are capable of passing through hundreds of light-years of metal and not even slowing down,”said Degrass Tyson.
But why are scientists even trying to catch them?
“When a supernova explosion occurs, the star collapses into itself and turns into a black hole. If this event occurs in our galaxy, then neutrino detectors like the same "Super-K" are able to catch the neutrinos emitted as part of this process. There are very few such detectors in the world,”explains Yoshi Uchida from Imperial College London.
Before a star collapses, it ejects neutrinos in all directions of space, and laboratories like Super-Kamiokande serve as early warning systems that tell scientists which direction to look to see the very last moments of star life.
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“Simplified calculations say that events of a supernova explosion in the radius in which our detectors can detect them, occur only once every 30 years. In other words, if you miss one, you will have to wait an average of several decades before the next event,”says Uchida.
The Super-K neutrino detector doesn't just pick up neutrinos that hit it directly from space. In addition, neutrinos are transmitted to it from the T2K experimental facility located in the city of Tokai, in the opposite part of Japan. The sent neutrino beam has to travel about 295 kilometers, after which it enters the Super-Kamiokande detector located in the western part of the country.
Observing how neutrinos change (or oscillate) as they travel through matter can tell scientists more about the nature of the universe, such as the relationship between matter and antimatter.
“Our Big Bang models suggest that matter and antimatter had to be created in equal proportions,” Morgan Vasco of Imperial College London told Business Insider.
“However, the main part of antimatter, for some reason or another, disappeared. There is much more ordinary matter than antimatter."
Scientists believe that the study of neutrinos may be one of the ways through which the answer to this riddle will finally be found.
How Super Kamiokande catches neutrinos
Located 1,000 meters underground, Super Kamiokande is something like this, the size of a 15-storey building.
Schematic of the Super-Kamiokande neutrino detector.
A huge cylinder-shaped stainless steel tank is filled with 50 thousand tons of specially purified water. Passing through this water neutrino moves at the speed of light.
"Neutrinos entering the reservoir produce light in a pattern similar to how the Concorde broke the sound barrier," says Uchida.
“If the plane is moving very quickly and breaks the sound barrier, then a very powerful shock wave is created behind it. Similarly, neutrinos passing through water and moving faster than the speed of light creates a light shock wave,”the scientist explains.
There are just over 11,000 special gilded "bulbs" installed on the walls, ceiling and bottom of the tank. They are called photomultipliers and are very light sensitive. It is they who capture these light shock waves created by the neutrinos.
Photomultipliers look like this.
Morgan Vasco describes them as "back light bulbs". These devices are so supersensitive that even with the help of one light quantum they are able to generate an electrical impulse, which is then processed by a special electronic system.
Do not drink water, you will become a kid
For light from shock waves generated by neutrinos to reach the sensors, the water in the tank must be crystal clear. So clean that you can't even imagine. At Super-Kamiokanda, it goes through a constant process of special multi-level cleaning. Scientists even irradiate it with ultraviolet light to kill all possible bacteria in it. As a result, she becomes such that she already takes horror.
“Ultra-purified water can dissolve anything. Ultra-purified water is a very, very unpleasant thing here. It has acid and alkali properties,”says Uchida.
“Even a drop of this water can cause you so much trouble that you never dreamed of,” adds Vasco.
People sail on a boat inside the Super-Kamiokande reservoir.
If it is necessary to carry out maintenance inside the tank, for example, to replace failed sensors, the researchers have to use a rubber boat (pictured above).
When Matthew Malek was a graduate student at the University of Sheffield, he and two other students were "lucky" to undertake similar work. By the end of the working day, when it was time to go upstairs, a specially designed drop-down gondola broke down. The physicists had no choice but to return to the boats and wait for it to be repaired.
“I didn't immediately understand when I was lying on my back in this boat and talking to others, how a tiny part of my hair, literally no more than three centimeters in length, touched this water,” says Malek.
As they floated inside the Super-Kamiokande and the scientists upstairs repaired the gondola, Malek was not worried about anything. He became worried early the next morning, realizing that something terrible had happened.
“I woke up at 3 am from an unbearable itch on my head. It was probably the worst itch I have ever experienced in my life. Worse than chickenpox, which I had as a child. It was so terrible that I simply could not sleep anymore,”the scientist continued.
Malek realized that a drop of water that fell on the tip of his hair "sucked dry" all nutrients from them and their deficiency reached his skull. He rushed to the shower in a hurry and spent more than half an hour there, trying to get his hair back.
Another story was told by Vasco. He heard that in 2000, during maintenance, personnel flushed water from the tank and found the outline of a wrench at the bottom.
“Apparently this key was accidentally left by one of the employees when they filled the tank with water in 1995. Having flushed water in 2000, they found that the key had dissolved."
Super-Kamiokande 2.0
Despite the fact that Super-Kamiokande is already a very large neutrino detector, scientists have proposed to create an even larger installation called Hyper-Kamiokande.
“If we get approval for the construction of Hyper-Kamiokande, then the detector will be ready for operation around 2026,” says Vasco.
According to the proposed concept, the Hyper-Kamiokande detector will be 20 times larger than the Super-Kamiokande. It is planned to use about 99,000 photomultipliers.
Nikolay Khizhnyak