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The Super-Kamiokande Neutrino Observatory Contains Ultrapure Water that Can Dissolve Metal and Detect Supernovas


Located 3,300 feet underground and fitted with around 13,000 giant orange bulbs, the Super-Kamiokande Neutrino Observatory looks like a supervillain’s lair straight out of a sci-fi movie. Buried under a mountain in Japan and as tall as a 15-story building, this high-end facility is part of a physics experiment that is helping scientists detect neutrinos, which are subatomic particles that can pass through solid objects and travel through space. Studying and observing these particles can actually help scientists detect supernovas. Another fascinating thing about the “Super-K” is that it contains ultrapure water that can even dissolve metal!

Buried under Mount Ikeno, the Super-Kamiokande neutrino detector is as tall as a 15-story building. The tank-shaped superstructure is fitted with around 13,000 photomultiplier tubes and is filled with ultrapure water.

Kamioka Observatory
Image credits: Kamioka Observatory, ICRR, University of Tokyo

Often abbreviated as “SK” or “Super-K,” the Super-Kamiokande Neutrino Observatory is located 1,000 meters or 3,300 feet below the ground in Japan’s Mozumi Mine. The superstructure is made up of a 136-foot-tall and 129-foot-wide cylindrical, stainless steel tank that holds up to 50,000 tons of ultrapure water. The tank is divided into two sections – an inner detector or “ID” region and an outer detector or “OD” region. The ID region is 119 feet tall and 111 feet wide. The OD region covers the rest of the tank volume. Around 13,000 photomultiplier tubes are fitted on the walls, roof, and floor of the cylinder-shaped superstructure. A blacksheet and Tyvek barrier is used to keep the OD and ID regions optically separate.

The current Kamioka Observatory is a successor of the Institute for Cosmic Ray Research, which is part of the University of Tokyo. The construction of the original facility started in 1982 and finished in 1983. The observatory was originally built to find out whether proton decay actually exists. It is one of the most fundamentally crucial questions in elementary particle physics.


Capable of detecting high-energy neutrinos, the Super-Kamiokande Observatory can solve some important mysteries of particle physics and tell us about what makes up our universe.

Cosmic Neutrino
Image credits: NASA’s Goddard Space Flight Center

The subatomic particles called neutrinos are all around us and passing through us at all times. Experts say that every second, approximately 65 billion neutrinos pass through each square centimeter of space. Despite their abundant existence, neutrinos are highly elusive. That is because they are extremely tiny and have no electric charge. As a result, we cannot use electromagnetic forces to detect or study these particles. According to Neil DeGrasse Tyson, neutrinos are capable of passing through “…a hundred lightyears of steel without even slowing down.”

Now, thanks to the Super-K observatory, scientists can finally trap and study these elusive particles. You might wonder why catching neutrinos is so important. Detecting these high-energy particles is the first step towards understanding proton decay and studying atmospheric and solar neutrinos. Moreover, the Super-Kamiokande Observatory will also detect stellar explosions called “supernovae.” Simply put, if a star in our galaxy explodes and becomes a black hole, the Super-K observatory will be able to detect the neutrinos that will be released as a result of that cosmic event. Supernova explosions are also rare events. Scientists predict that within the range that the Super-K covers, such an event may occur once every 30 years. So, if they miss it once, they would have to wait three more decades to study the next one!


The method of catching these neutrinos is also fascinating. It is achieved through the combination of ultrapure water and photomultiplier tubes.

Kamioka Observatory
Image credits: Kamioka Observatory, ICRR, University of Tokyo

As mentioned above, the cylindrical structure holds 50,000 tons of ultra-pure water. When a neutrino interacts with the electrons of water, it produces a charged particle that is capable of moving faster than the usual speed of light in water. Now, imagine this – if a plane travels faster than the speed of sound, it is likely to produce a big shockwave. It will create a much louder noise than a plane that is flying at a normal speed.

Similarly, when neutrinos travel faster than the speed of light in water, they produce a shockwave or a cone of light called “Cherenkov radiation.” This shockwave is then picked up by the photomultiplier tubes that look like giant golden bulbs. The photomultiplier tubes are sort of like the opposite of regular bulbs. Instead of giving out light, they are incredibly good at detecting even the tiniest amount of light and turning it into electrical current. This way, the super-elusive neutrinos become visible.

The water inside the tank is so pure that it can leach the nutrients out of your hair and even dissolve metal!

Kamioka Observatory
Image credits: Kamioka Observatory, ICRR, University of Tokyo

The water inside the tank needs to be ultrapure. Otherwise, the photomultiplier tubes will not be able to pick up the faint light waves. The water is constantly filtered and re-purified and even blasted with UV lights for the removal of bacteria and other impurities. This ultrapure water actually has the qualities of alkaline and acid. That means, if you were to get soaked in this water, you would experience a significant amount of exfoliation. That is why the researchers and the maintenance crew always use rubber dinghies.

One time, while doing some maintenance work inside the tank, a physicist accidentally dipped the tip of his hair into the water. Later that night, he was awoken by the worst scalp itch ever. Unable to go back to sleep, he realized that the hair must have gotten wet, and the water had leeched the nutrients from his hair and scalp. He immediately got up and vigorously conditioned his hair to remedy the situation. Another researcher stated that when the tank was fully drained in the year 2000, they discovered the outline of a wrench on the floor. That can only mean one thing – when the tank was filled up in 1995, somebody had mistakenly left a wrench behind, and in a matter of five years, the ultrapure water had completely dissolved the metal tool!

A better and more advanced neutrino observatory is currently in the process of being constructed near Kamioka in Japan.

If the Super-Kamiokande seems impressive now, the Hyper-Kamiokande is sure to leave the world stunned. The new facility would be part of the Kamioka Observatory, and it is said to be 20 times larger than the Super-K. The construction will begin in April 2020.

(Sources: 1, 2, 3, 4)


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