Screening and Relativistic Effects on Beta-Spectra

The effect of screening by atomic electrons on the form of allowed beta-ray spectra of the Fermi theory is calculated approximately, with the assumption of a screened potential based on the Thomas-Fermi model of the atom. The apparent deviation from theory caused by neglecting screening is given for the beta-emitters ${\mathrm{S}}^{35}$, ${\mathrm{Cu}}^{64}$, and RaE. Another smaller source of error in interpreting experimental results is the use of the non-relativistic approximation to the Coulomb correction factor. These effects cannot be neglected in an accurate analysis of data for Cu and heavier elements.