Two years later, Maurice Goldhaber, Lee Grodzins and Andrew Sunyar measured the "handedness" of neutrinos in an ingenious experiment at the Brookhaven National Laboratory in the US. These electrons create flashes of Cerenkov light that are detected by the 9600 photomultiplier tubes surrounding the vessel. A few of the neutrinos that pass through the detector interact to produce electrons that travel faster than the speed of light in the heavy water. The vessel is 12 metres across and is filled with 1000 tonnes of heavy water. When their result was announced, Pauli kept his promise.Ī view of the SNO detector located 2000 metres underground in the Creighton mine near Sudbury, Canada. Indeed this was the case until 1956, when Clyde Cowan and Fred Reines detected antineutrinos emitted from a nuclear reactor at Savannah River in South Carolina, USA. Being Italian, "neutrino" was the obvious choice: a little neutral one.īecause neutrinos interact so weakly with matter, Pauli bet a case of champagne that nobody would ever detect one. Since Chadwick had taken the name "neutron" for something else, Fermi had to invent a new name. However, Pauli's particle played a crucial role in the first theory of nuclear beta decay formulated by Enrico Fermi in 1933 and which later became known as the weak force. Two years later, James Chadwick discovered what we now call the neutron, but it was clear that this particle was too heavy to be the "neutron" that Pauli had predicted. Dubbed the "neutron" by Pauli, the new particle would be emitted together with the electron in beta decay so that the total energy would be conserved. Pauli's remedy was to introduce a new neutral particle with intrinsic angular momentum or "spin" of (1/2)*h/2π, where h is Planck's constant. Unable to attend a physics meeting in December 1930, he instead sent a letter to the other "radioactive ladies and gentlemen" in which he proposed a "desperate remedy" to save the law of energy conservation. The finding even led Niels Bohr to speculate that energy may not be conserved in the mysterious world of nuclei. This came as a great surprise to many physicists because other types of radioactivity involved gamma rays and α-particles with discrete energies. After much confusion and debate, the energy of the radiated electron was found to follow a continuous spectrum. In beta decay, a neutron in an unstable nucleus transforms into a proton and emits an electron at the same time. At the time physicists were puzzled because nuclear beta decay appeared to break the law of energy conservation. Neutrinos have been shrouded in mystery ever since they were first suggested by Wolfgang Pauli in 1930.
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