On the Fermi Theory of Beta Radioactivity

A comparison of Fermi's formula for the distribution in energy of the electrons and positrons emitted by radioactive bodies with the observed spectra seems to show that a basic factor in it, the statistical factor, is not asymmetric enough. Since about the same degree of asymmetry is common to the spectra of light and heavy nuclei and of positron and electron emitters, it cannot be ascribed to another factor in the Fermi formula, depending on the nuclear field. A weight factor is introduced to provide the required asymmetry by changing the form of the Fermi interaction energy. It is shown that two almost equivalent points of view can be employed in attacking this problem and that a certain uniqueness in the form of the interaction law can be obtained within the requirements laid down by Fermi. The modified distribution formula, which holds strictly only for light nuclei, is then shown to give a much more satisfactory agreement with the data than the original formula.