Shape of Beta Spectra of Once Forbidden Transitions in the Decays ofGa72,La140,Eu152,Eu154, andSb124

Magnetic spectrometer studies were made on the beta spectra of ${\mathrm{Ga}}^{72}$, ${\mathrm{La}}^{140}$, ${\mathrm{Eu}}^{152}$, ${\mathrm{Eu}}^{154}$, and ${\mathrm{Sb}}^{124}$. The highest energy beta group of each of these transitions has an abnormally long comparative half-life and probably is a once forbidden decay from a 3- initial state to a 2+ final state. For all, the highest energy beta spectrum was found to have a nonstatistical, nonunique shape. On the assumption that the $B_{\mathrm{ij}}$ matrix element dominates the decay, the experimental shape factors were fitted empirically by $C=q^2+\lambda p^2+D$. The best fits were obtained for values of $D$ equal to 15, 10, 5, 20, and 15 for ${\mathrm{Ga}}^{72}$, ${\mathrm{La}}^{140}$, ${\mathrm{Eu}}^{152}$, ${\mathrm{Eu}}^{154}$, and ${\mathrm{Sb}}^{124}$, respectively.