日本一個埋在山下的金室裡的水如此純淨，它可溶解金屬及正在幫助科學家探測垂死的恆星
A golden chamber buried under a mountain in Japan contains water so pure it can dissolve metal, and it's helping scientists detect dying stars
April 18, 2020
The neutrino detector Super-Kamiokande.
Kamioka Observatory, ICRR (Institute for Cosmic Ray Research), The University of Tokyo
- The Super-Kamiokande neutrino detector is a physics experiment the size of a 15-story building, buried under a mountain in Japan.
- Neutrinos are sub-atomic particles that pass through us all the time, and studying them can tell us about supernovas and the composition of the universe.
- Super-Kamiokande featured on the cover of Nature Magazine in April 2020 after the detector played a vital part in a paper examining the relationship between matter and anti-matter.
- The detector is full of ultra-pure water, which can leach the nutrients out of your hair and dissolve metal.
Hidden 1,000 metres under Mount Ikeno in Japan is a place that looks like a supervillain's dream.
Super-Kamiokande (or "Super-K" as it's sometimes referred to) is a neutrino detector. Neutrinos are sub-atomic particles which travel through space and pass through solid matter as though it were air.
Studying these particles is helping scientists detect dying stars and learn more about the universe. Business Insider spoke to three scientists about how the giant gold chamber works — and the dangers of conducting experiments inside it.
Related Video: What if Humans Tried Landing on the Sun
Seeing the sub-atomic world
Neutrinos can be very hard to detect, so much so that Neil deGrasse Tyson dubbed them "the most elusive prey in the cosmos." In this video, he explains that the detection chamber is buried deep within the earth to stop other particles from getting in.
"Matter poses no obstacle to a neutrino," he says. "A neutrino could pass through a hundred light-years of steel without even slowing down."
But why catch them at all?
"If there's a supernova, a star that collapses into itself and turns into a black hole," Dr Yoshi Uchida of Imperial College London told Business Insider. "If that happens in our galaxy, something like Super-K is one of the very few objects that can see the neutrinos from it."
Before a star starts to collapse it shoots out neutrinos, so Super-K acts as a sort of early-warning system, telling us when to look out for these dazzling cosmic events.
NASA, ESA, G. Dubner (IAFE, CONICET-University of Buenos Aires) et al.; A. Loll et al.; T. Temim et al.; F. Seward et al.; VLA/NRAO/AUI/NSF; Chandra/CXC; Spitzer/JPL-Caltech; XMM-Newton/ESA; and Hubble/STScI
"The back-of-the-envelope calculations say it's going to be about once every 30 years that a supernova explodes in the sort of range that our detectors can see," said Dr Uchida. "If you miss one you're going to have to wait another few decades on average to see the next one."
Firing neutrinos through Japan
Super-K doesn't just catch neutrinos raining down from space.
Situated on the opposite side of Japan in Tokai, the T2K experiment fires a neutrino beam 295 km through the Earth to be picked up in Super-K on the west side of the country.
Studying the way the neutrinos change (or "oscillate") as they pass through matter may tell us more about the origins of the universe.
In April 2020 Super-Kamiokande featured on the cover of Nature magazine following a breakthrough using the detector which brought researchers closer to understanding the relationship between matter and anti-matter.
Kamioka Observatory, ICRR (Institute for Cosmic Ray Research), The University of Tokyo
"Our big bang models predict that matter and anti-matter should have been created in equal parts," Dr Morgan Wascko of Imperial College told Business Insider, "but now [most of] the anti-matter has disappeared through one way or another."
Researchers fired neutrinos and anti-neutrinos at Super-Kamiokande to study how they oscillated. According to Imperial, the researchers' findings provide the "strongest evidence yet" that matter and antimatter behave differently, explaining why the two wouldn't immediately annihilate each other at the beginning of the universe.
"This result brings us closer than ever before to answering the fundamental question of why the matter in our universe exists. If confirmed – at the moment we're over 95 percent sure – it will have profound implications for physics and should point the way to a better understanding of how our universe evolved," said Dr Patrick Dunne, a physicist at Imperial college.
How Super-K catches neutrinos
Kamioka Observatory, ICRR (Institute for Cosmic Ray Research), The University of Tokyo
Buried 1,000 metres underground, Super-Kamiokande is as big as a 15-story building.
The enormous tank is filled with 50,000 tonnes of ultra-pure water. This is because when travelling through water, neutrinos are faster than light. So when a neutrino travels through water, "it will produce light in the same way that Concord used to produce sonic booms," said Dr Uchida.
"If an aeroplane is going very fast, faster than the speed of sound, then it'll produce sound — a big shockwave — in a way a slower object doesn't. In the same way a particle passing through water, if it's going faster than the speed of light in water, can also produce a shockwave of light."
The chamber is lined with 11,000 golden-coloured bulbs. These are incredibly sensitive light-detectors called Photo Multiplier Tubes (PMTs) which can pick up these shockwaves.
Here's a closeup of a PMT:
Dr Wascko describes them as "the inverse of a lightbulb." Simply put, they can detect even minuscule amounts of light and convert it into an electrical current, which can then be observed.
Terrifyingly pure water
In order for the light from these shockwaves to reach the sensors, the water has to be cleaner than you can possibly imagine. Super-K is constantly filtering and re-purifying it, and even blasts it with UV light to kill off any bacteria.
Which actually makes it pretty creepy.
"Water that's ultra-pure is waiting to dissolve stuff into it," said Dr Uchida. "Pure water is very, very nasty stuff. It has the features of an acid and an alkaline."
"If you went for a soak in this ultra-pure Super-K water you would get quite a bit of exfoliation," said Dr Wascko. "Whether you want it or not."
When Super-K needs maintenance, researchers need to go out on rubber dinghies to fix and replace the sensors.
Kamioka Observatory, ICRR (Institute for Cosmic Ray Research),The University of Tokyo
more:
https://www.yahoo.com/news/golden-chamber-buried-under-mountain-142000374.html
超級神岡探測器
超級神岡探測器（英語：Super-Kamiokande，可縮寫為Super-K或SK；日語：スーパーカミオカンデ），全名為超級神岡微中子探測實驗（Super-Kamioka Neutrino Detection Experiment），是日本東京大學在岐阜縣飛驒市神岡町的神岡礦山（日語：神岡鉱山）一個深達1000米的廢棄砷礦中建造的大型微中子探測器。其目標是探測質子衰變[2][3][4][5][6][7][8]以及被設計來尋找太陽、地球大氣的微中子，並觀測銀河系內超新星爆發。目前超級神岡的後續項目，更先進的下一代超巨型神岡探測器（英語：Hyper-Kamiokande，可縮寫為HK）正在進行預研，預計於2020年四月開工建設。https://zh.m.wikipedia.org/zh-tw/%E8%B6%85%E7%BA%A7%E7%A5%9E%E5%86%88%E6%8E%A2%E6%B5%8B%E5%99%A8
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