Anomalousεβ+Decay Branching Ratios: A Theoretical Explanation

Anomalous $\frac{\epsilon }{{\beta }^{+}}$ branching ratios for hindered allowed transitions in ${}_{}{}^{145}{}_{}{}^{}\mathrm{Gd}$ and ${}_{}{}^{143}{}_{}{}^{}\mathrm{Sm}$ decay are explained in terms of second-order corrections to normal allowed theory. These calculations lead to correction factors as large as 1000 in nuclei near $Z=80\mathrm{}$, and explain a smaller anomaly for ${}_{}{}^{22}{}_{}{}^{}\mathrm{Na}$ decay. A simplified equation is presented to estimate skew ratios, $\frac{{\left(\frac{\epsilon }{{\beta }^{+}}\right)}_{\mathrm{expt}}}{{\left(\frac{\epsilon }{{\beta }^{+}}\right)}_{\mathrm{theor}}}$, for moderately hindered transitions.