![]() ![]() The difference is 1.293MeV, and the proton gets so little kinetic energy that we can ignore it. It spits out an electron and an antineutrino and becomes a proton with a mass-energy of 938.272MeV. We start with a neutron with a mass-energy of 939.565MeV. See Rod Nave’s hyperphysics for a picture: Image from Rod Nave’s hyperphysics It goes on to say that in 1914 James Chadwick made more accurate measurements which showed that the spectrum was continuous, and that in 1933 Charles Ellis and Nevill Mott demonstrated that the beta spectrum has an upper bound. It says: “these measurements offered the first hint that beta particles have a continuous spectrum”. See the Wikipedia beta decay article which talks about early work by Lise Meitner and Otto Hahn in 1911, and by Jean Danysz in 1913. The electron kinetic energy varies in a smooth continuous fashion, such that there’s a “spectrum” of electron kinetic energies. However most of the time the electron is emitted as a fast-moving beta particle: Beta decay image from CSIRO, see The Sun: Energy from Nuclei In circa four cases per million the proton and electron remain bound as a hydrogen atom, because the electron had very little kinetic energy. Some part of the neutron suffers some kind of partial annihilation, resulting in an electron and its half-brother the antineutrino. That’s an antineutrino rather than a neutrino, but no matter. Outside of a nucleus the neutron decays in about 15 minutes into a proton, an electron, and an antineutrino: n → p + e – + v̄ e. Talking of which, perhaps the cleanest example of beta decay is free neutron decay. Electrons are called fermions because of Fermi. That’s why he became “the architect of the nuclear age”. Because of that rejection, Fermi took a break from theoretical physics and did some experimental physics. He came up with a paper on beta decay in 1933 which Nature rejected, see the English translation at MicroBooNE prefaced by Fred Wilson. Amaldi was joking, but Fermi wasn’t, and the name stuck. Hence the name was changed from neutron to neutrino by Edoardo Amaldi and Enrico Fermi. This was the name given to the neutron proper by James Chadwick in 1932. He talked about a particle that travels slower than light, and he called it a neutron. He was wrong about some other things too. I have postulated a particle that cannot be detected”. Pauli later said “ I have done a terrible thing. You can find his original letter to Lise Meitner and others on the Fermilab MicroBooNE database, along with the English translation: The neutrino was proposed by Wolfgang Pauli in 1930 to account for the conservation of energy and spin angular momentum in beta decay.
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