Seventy years ago, Physicists Clyde Cowan and Frederic Rense took a custom-built 10-ton detector, surrounded it with thick lead walls and wet sandbags, and placed it near a powerful nuclear reactor at the Savannah River plant in South Carolina. They called the experiment “Project Poltergeist,” designed to catch a ghost.
More than a quarter century ago, physicists were puzzling over why energy was lost during a radiation process called beta decay. Something was missing, and there was no known physics to explain it. Then in 1930, Austrian physicist Wolfgang Pauli proposed a radical solution: a virtually undetectable particle was silently carrying the lost energy away. “I did a terrible thing,” Paulie told a friend. “I assumed the existence of an undetectable particle.” It will be known as the neutrino. Because they have almost no mass or charge, these particles can pass through the Earth and everything on it, including our bodies, almost unhindered.
The massive device used by Cowan and Reines in early 1956 was intended to find what Pauli thought was impossible. In June of that year, the pair were physicists from Los Alamos National Laboratory Paulie sent a telegram: “We are pleased to inform you that we have definitely detected neutrinos.”
Then attention turned to a broader question. If nuclear reactions produce neutrinos, can we use them to observe nuclear fireworks inside stars, including the Sun? This presented a major challenge: How do you capture particles emitted by distant stars if these particles can pass through almost anything without being detected? The suspicion was that detecting a particle that rarely collides with matter would require an enormous amount of matter to collide with it. Furthermore, the material must be protected from the noise of other forms of radiation. So the answer scientists came up with was to build some of the biggest, deepest, and strangest experimental traps in scientific history… and then they waited.
In the 1960s, Raymond Davis Jr. and his colleagues at Brookhaven National Laboratory placed a tank 1.5 kilometers underground in the Homestake Mine in South Dakota and filled it with nearly 400,000 liters of a chlorine-based cleaning fluid called perchlorethylene. On the rare occasions that a passing neutrino collides with a chlorine nucleus, it turns into a radioactive form of argon that can be detected and counted. The experiment, which will last 25 years, has found a third of the number of neutrinos coming from the Sun that were predicted in theoretical models. This became known as the solar neutrino problem.
It would be decades before the problem was solved by more massive experiments. Deep in the Kamioka mine in Japan, Masatoshi Koshiba built a different type of detector called Kamiokandi, which uses 3 million liters of ultra-pure water. In this setup, neutrinos sometimes interact with atomic nuclei in water. The reaction creates an electron that moves very quickly, generating a flash of what is called Cherenkov light. This light is captured by detectors.
Kamiokande and Koshiba confirmed the deficiency discovered by Davis, and a second, larger detector, Super Kamiokande, as well as Canada’s Sudbury Neutrino Observatory, also clarified the discrepancy. Neutrinos come in three different “flavors” (electron, muon, and tau) and can oscillate or switch between them. To do this, neutrinos must have mass, which the laws of physics failed (and still fail) to predict.
Newer neutrino detectors continue the tradition of grand ambitions and surprising results. the IceCube Neutrino Observatory Below the Amundsen-Scott Antarctic station, Antarctic ice is used instead of water. A. has developed The map of the Milky Way is made up of neutrinos only They traced these high-energy cosmic particles to active galaxies powered by supermassive black holes. On the bottom of the Mediterranean Sea Cubic kilometer neutrino telescope KM3NET discovered the highest energy cosmic neutrino ever. Its source remains unknown.
