Nestled deep in the ground near a quiet mountainous city in the heart of Japan lies one of the world’s most astounding neutrino detectors.
The Super-Kamiokande neutrino detector sits 3,300 feet below the ground on Mount Ikeno, underneath an old mine located in the Kamioka area near the city of Hida.
Nicknamed Super-K, the impressive structure towers up to a height of 15 stories and uses extremely pure water to find neutrinos. This helps researchers detect dying stars and find answers to the most pressing questions about the Universe, such as “Where does matter come from?”
What Are Neutrinos?
Neutrinos are the most mysterious subatomic particles known to man. Billions of them stream through space every day. In fact, many of them pass through the Earth and every physical object on it without humans ever feeling their effects. That is because neutrinos pass through matter without leaving a trace.
Researchers say a neutrino can pass through metal for 100 light-years and not be affected by it at all. Without special equipment, it is practically impossible for scientists to detect even the slightest whiff of this elusive particle.
Super-K Can Detect A Supernova
Neutrinos are, however, known to appear in numbers when a star reaches the last stages of its life and falls in on itself in a last brilliant display of light and energy before it morphs into a black hole. Only a neutrino detector like Super-K can spot the neutrinos being fired off from them.
“If that happens in our galaxy, something like Super-K is one of the very few objects that can see the neutrinos from it,” says Yoshi Uchida of Imperial College London.
Explosions like these, called supernovas, happen only 30 years. If scientists do not have the sort of early warning system that Super-K can provide, then they may have to wait three or more decades before they can observe the next star explosion.
Researchers also use Super-K to probe into the deepest of cosmic mysteries. Morgan Wascko, also of Imperial College London, studies the oscillations neutrinos make when they pass through matter in an attempt to understand the origin of matter and anti-matter.
How Super-K Detects Neutrinos
Super-K is filled with 50,000 tonnes of ultra-pure water. That is about more water that can fill eight Olympic-sized swimming pools. When neutrinos pass through water, they speed up so much that they can travel at the speed of light.
At this rate, they also produce light, in the same way, the supersonic jet Concorde produced a sonic boom when it broke the sound barrier.
Along the walls of Super-K are 11,000 golden-colored bulbs called Photo Multiplier Tubes, which are essentially light bulbs turned inside-out. They can detect the light produced by high-speed neutrinos and convert it into electrical currents that can then be observed by scientists.
Very, Very Nasty Water
For the bulbs to be able to detect the light, the water in Super-K has to be kept as pure and clean as possible through constant filtering and purification using ultraviolet light. However, super-clean water is not as pleasant as most people may think.
The researchers say it actually has the properties of an acid and an alkaline combined into one.
“If you went for a soak in this ultra-pure Super-K water you would get quite a bit of exfoliation,” Wascko says, putting it lightly.
Maintenance crews, for instance, have to ride a rubber boat to replace worn out sensors. In 2000, when Super-K was drained, they found the outline of a wrench at the bottom of the chamber. It had been left there from 1995 when the neutrino detector was first filled with water.
Matthew Malek, a researcher at the University of Sheffield, accidentally dipped not more than 3 centimeters of his hair in the water. The next day, Malek woke up to an extremely itchy scalp, a sign that the water has seeped into his hair and sucked off the nutrients.
Formidable as it may seem, Super-K may be about to be eclipsed by an even grander structure. If plans for construction are approved, the Japanese will build Hyper-Kamiokande, which is set to go into operation in 2026. The future neutrino detector will be 20 times larger in volume and will have 99,000 light detectors.