Accurate measurements of $L$-shell internal-conversion line intensity ratios are reported for four low-energy $E2\mathrm{}$ transitions in ${}_{}{}^{156}{}_{}{}^{}\mathrm{Gd}$, ${}_{}{}^{160}{}_{}{}^{}\mathrm{Dy}$, ${}_{}{}^{166}{}_{}{}^{}\mathrm{Er}$, and ${}_{}{}^{170}{}_{}{}^{}\mathrm{Yb}$. The measurements were made using a 100-cm radius iron-free $\pi \sqrt{2}$ double-focusing $\beta$ spectrometer at resolution settings of 0.03-0.09% in momentum. Different source and detector arrangements were used to explore for possible systematic effects. In all cases the experimental $\frac{L_{\mathrm{II}}}{L_{\mathrm{III}}}$ intensity ratios agreed with the corresponding theoretical ratios to ≤2%. The $\frac{L_{\mathrm{I}}}{L_{\mathrm{II}}}$ and $\frac{L_{\mathrm{I}}}{L_{\mathrm{III}}}$ experimental ratios are systematically larger than the theoretical values by an average of 5.4%.

• Received 16 January 1967

DOI:https://doi.org/10.1103/PhysRev.157.1043