Earth and the Moon


If neutrinos are so elusive, how do scientists observe them striking Earth?

Fortunately, neutrinos are so unlikely to interact with any matter—including the atoms and molecules in the human body—that the billions upon billions of neutrinos that hit you every second have no discernible effect. In fact, the odds that any neutrino striking Earth will interact with any atom in our planet at all is about one in a billion. Even when it does happen, the result is merely a tiny flash of harmless light.

It is possible to detect neutrinos from space by their very rare interactions with matter here on Earth, but not with conventional telescopes. The first effective neutrino detector was set up in 1967 deep underground in the Homestake Gold Mine near Lead, South Dakota. There, the American scientists Ray Davis, Jr. (1914–2006) and John Bahcall (1934–2005) set up a tank filled with 100,000 gallons of nearly pure perchlorate (used as dry-cleaning fluid), and monitored the liquid for very rare neutrino interaction events. In 2002, Ray Davis, Jr., was awarded the Nobel Prize in Physics. Other experiments have since used other substances, such as pure water, for neutrino detections.


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