<sod>During the 1910s and 1920s, through the study of electron spectra from the nuclear [[beta decay]], it became apparent that, in addition to an electron, another particle with very small mass and with no electric charge is emitted in the beta-decay but not observed. The observed electron energy spectrum was continuous. Assuming energy conservation, this is only possible if the beta decay is a three-body rather than a two-body decay: the latter produces monochromatic peak rather than a continuous energy spectrum. This and other reasons led [[Wolfgang Pauli]] to postulate the existence of the neutrino in 1930.<eod>
<sod>During the 1910s and 1920s, through the study of electron spectra from the nuclear [[beta decay]], it became apparent that, in addition to an electron, another particle with very small mass and with no electric charge is emitted in the beta-decay but not observed. The observed electron energy spectrum was continuous. Assuming energy conservation, this is only possible if the beta decay is a three-body rather than a two-body decay: the latter would produce a monochromatic peak rather than a continuous energy spectrum. This and other reasons led [[Wolfgang Pauli]] to postulate the existence of the neutrino in 1930.<eod>