ABSTRACT
This chapter discusses the classical theory of weak interaction, based on Fermi’s theory of 1934, and also touch on its historical development. It firstly explains what we understand by relativistic interaction currents. The classical theory of the weak interaction, which resulted from Fermi’s current–current ansatz has proved to be a good description of most low-energy weak interaction processes. In particular, it predicts the energy spectra and the angular correlations of nuclear beta decay and of μ decay with great accuracy. The chapter also discusses some elementary characteristics of nuclear beta decay. Fermi and Gamow–Teller transitions, which together are classified as allowed beta decays, not only determine the decay of the neutron but also dominate that of most nuclei, insofar as these transitions are permitted by the selection rules to be discussed.
