|The enigma of the missing energy of beta électrons|
Around 1930, beta decay was considered to produce two particles: the recoiling nucleus and an electron. Like in alpha decay, it was supposed to be a ‘monokinetic’ reaction, with the electron carrying away all of the available energy. Beta decay, however, produced a wide spectrum of possible and smaller energies for the electron, as the above figure shows. Where did the missing energy go? When confronted with this dilemma, Niels Bohr went so far as to ask himself whether or not the law of conservation of energy was still valid.