ABSTRACT
The idea of the neutrino arose due to problems encountered during the early days of beta decay. The beta decay spectra were continuous instead of discrete and the the spins did not add up. For example in the decay 14C−→14 N+e−, the initial particle is in a spin 0 state, while the two decay states are in spin 1 and spin 1/2 respectively (Scott 1935). Bohr suggested that maybe energy and momentum were not conserved in beta decay. In a famous letter to Lise Meitner presented at a worshop in Tu¨bingen in 1930, Pauli made a radical proposal:
“I have hit upon a desperate remedy to save the “exchange theorem” of statistics and the law of conservation of energy. Namely, the possibility that there could exist in the nuclei electrically neutral particles, that I wish to call neutrons, which have spin 1/2 and obey the exclusion principle and which further differ from light quanta in that they do not travel with the velocity of light. The mass of the neutrons should be of the same order of magnitude as the electron mass and in any event not larger than 0.01 proton masses.”
