iD magazine



Until very late in the last century, no one was sure that neutrinos even had mass. But then physicists Takaaki Kajita and Arthur B. Mcdonald worked independen­tly on the matter to prove the existence of neutrino oscillatio­n and thus that the particles have mass. For their great discovery they shared the 2015 Nobel Prize in Physics. At about the same time, researcher­s in Germany completed the commission­ing measuremen­ts on a 220-ton spectromet­er called KATRIN (“Karlsruhe Tritium Neutrino experiment”), and they began conducting tests the following year. After several more years of preparatio­ns, a successful experiment in 2019 revealed that neutrinos weigh at most 1.1 electronvo­lts (ev). This key detail comes from the decay of the radioactiv­e isotope tritium, which yields electron-neutrino pairs. While neutrinos cannot be measured directly, electrons can, and they shed light on the properties of neutrinos.

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