We have measured the $N_{\mathrm{II}}$ and $N_{\mathrm{III}}$ conversion electrons from the $\approx 2.33$-keV transition in ${}_{}{}^{205}{}_{}{}^{}\mathrm{Pb}$ with a $\pi \sqrt{2}$, iron-free, double-focusing $\beta$-ray spectrometer and have determined the energy of this transition to be 2.328±0.007 keV. We obtain an $\frac{N_{\mathrm{II}}}{N_{\mathrm{III}}}$ ratio of 0.70±0.25 for this transition and a ratio $\frac{(N_{\mathrm{II}}+N_{\mathrm{III}})}{L_{\mathrm{I}}}$, where the $L_{\mathrm{I}}$ is from the 26.22-keV $M2\mathrm{}$ isomeric transition in${}_{}{}^{205}{}_{}{}^{}\mathrm{Pb}$, of ${0.48}_{-0.05\mathrm{}}^{+0.15\mathrm{}}$. These are in very good agreement with predicted conversion ratios and represent the first test of theoretical calculations for the $N$ shell at such low energies.

• Received 18 March 1971

DOI:https://doi.org/10.1103/PhysRevLett.26.1043