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A beta-decay spectrum gives the distribution of emitted electron or positron energies in beta decay. In ordinary three-body beta decay, the charged lepton shares the available energy with a neutrino and the recoiling daughter nucleus, producing a continuous spectrum.

For a simple allowed decay, its shape includes phase-space factors, an electron Coulomb correction and an endpoint set by the available energy. Schematically, $d\Gamma /dE\propto F(Z,E)pE(E_0-E{)}^2$ when the neutrino mass is neglected and $E$ is total electron energy. Nuclear matrix elements and forbiddenness can modify this expression. The continuum was central to understanding the missing energy carried by the neutrino.

An experimental nuclear physicist who coauthored a 1964 comparison of allowed and unique first-forbidden beta-decay spectrum shapes. A double-lens spectrometer measured the shapes of several isotope spectra, testing whether their energy dependence followed the simplest transition models. The report concerns specific indium, potassium, rubidium, strontium and yttrium isotopes; its conclusions should not be transferred to an arbitrary isotope without checking the transition.^[ref]