Weak interactions of the neutron

The most familiar manifestation of the weak interaction is nuclear beta decay and the most elementary beta -active nucleus is the neutron itself. The author examines the advantages and limitations of the various experimental techniques employed to study neutron beta decay and the implications of the results for fundamental theory and, to a lesser extent, for cosmology. The interaction responsible for nuclear beta decay is accurately described by a (V-A) theory with an absolute ratio of axial-vector to polar-vector coupling constants of mod lambda mod =1.257+or-0.009, and that the interaction is invariant under time reversal at the level of 10^-3. Although, somewhat surprisingly, there still exists a considerable measure of uncertainty as to the precise value of the neutron half-life, it is not unfair to suggest that much of the experimental data on neutron beta decay is essentially complete so far as it relates to the fundamental structure of the weak charged currents. On the existence of weak magnetism or on the presence or absence of second-class currents, neutron beta decay, as distinct from nuclear beta decay, has told us nothing to date, and significant advances in experimental technique are probably required before that information begins to flow.