Cross Terms in Allowed ShapeβSpectra

A statistical analysis is made of allowed shape $\beta$ spectra to determine the magnitude of any $\frac{1}{W}$ terms that may be present. Both allowed and first forbidden spectra are analyzed; only the allowed spectra are discussed here. It is concluded that the ($T, A$) mixture in $\beta$ decay is ≲4 percent. Unfortunately only one measurement can be used for the ($S, V$) mixture, and it does not limit the mixture to less than ∼10 percent. For neither ($T, A$) nor ($S, V$) is the mixture significantly different from zero.