In 1914, James Chadwick [Cha14] and others showed experimentally that the electron spectrum measured in beta decay was continuous instead of a single line expected in a two-body decay. This result has not been immediately accepted since it could be due to experimental or theoretical artifacts which could simulate the observed behavior of the electron spectrum. We had to wait until 1927, when Charles Drummond Ellis and William Alfred Wooster [Ell27] made a decisive experiment on radium E (bismuth-210), giving a direct proof that the electron spectrum was continuous. To face this contradiction, several important physicists, among them the famous Niels Bohr, suggested iconoclastically that energy was not conserved or was conserved “in the mean”. The debate about a possible violation of a fundamental law of physics remained for years, even after the Pauli’s proposal of the neutrino in 1930 [Pau30,Pau33]. It vanished naturally.
|Cha14||J. Chadwick||Intensitatsverteilung im magnetischen spektrum der b -strahlen von radium B+C||Verhandlungen der deutschen Physikalischen Gesellschaft 16 (1914) 383|
|Ell27||C.D. Ellis and W.A. Wooster||The Average Energy of Disintegration of Radium E||Proc. Roy. Soc. (A) 117 (1927) 109|
|Pau30||W. Pauli||Dear radioactive ladies and gentlemen||Pauli to L. Meitner , Pauli’ letter|
|Pau33||W. Pauli||Discussion du rapport de M. Heisenberg « Structure et propriétés des noyaux atomiques »||7ème Conseil Physique Solvay, Bruxelles, 1933, Gautier-Villars (1934) p. 324,|