ZDependence of Radiative Corrections toβDecay

We show that to first order in $\alpha$, and with neglect of effects which vanish in the limit of zero lepton momenta, the theoretical $\mathrm{ft}$ value in 0 → 0 Fermi transitions is independent of $Z$. The only model-dependent feature of this argument is in the treatment of effects induced by the axial current. It is further shown that in higher order radiative corrections the power of $Z$ cannot exceed the power of $\alpha$; the leading term in the radiative correction to the $\mathrm{ft}$ value is therefore of order $Z^2{\alpha }^2$.