Decays of the Even-Even Lead Isomers:Pb202mandPb204m

The decays of the $9^{-}$ isomers, ${}_{}{}^{202m}{}_{}{}^{}\mathrm{Pb}$ and ${}_{}{}^{204m}{}_{}{}^{}\mathrm{Pb}$, have been investigated using Ge(Li) detectors in a variety of singles and coincidence configurations. Improved conversion coefficients were obtained for two of the transitions following the decay of ${}_{}{}^{204m}{}_{}{}^{}\mathrm{Pb}$, but no new, weak transitions were seen. Considerable improvement and enlargement of the ${}_{}{}^{202m}{}_{}{}^{}\mathrm{Pb}$ decay scheme was possible. We have been able to make unambiguous multipolarity assignments for 15 of the 18 transitions following its decay and to place all 18 in a consistent decay scheme. States in ${}_{}{}^{202}{}_{}{}^{}\mathrm{Pb}$ were established (following the 90.5% isomeric-transition decay) at 0 ($J^{\pi }=0^{+}$), 960.70 ($2^{+}$), and 1382.82 ($4^{+}$), 1623.1 ($4^{+}$), 1915.2 ($4^{+}$), 2040.3 ($5^{-}$), and 2169.8 keV ($9^{-}$). Those in ${}_{}{}^{202}{}_{}{}^{}\mathrm{Tl}$ (following the 9.5% electron-capture decay) lie at 0 ($2^{-}$), 490.47 ($4^{-}$), 950.19 ($7^{+}$), 1098.7 ($6^{+}$, $7^{+}$, $8^{+}$), 1340.1 ($8^{+}$), 1552.1 ($8^{+}$ [$9^{+}$]), and 1675.6 keV ($9^{+}$, $8^{+}$). Interpretation is made concerning the nature of the states in ${}_{}{}^{202}{}_{}{}^{}\mathrm{Pb}$ and even-even Pb isotopes and also in ${}_{}{}^{202}{}_{}{}^{}\mathrm{Tl}$ and odd-odd Tl isotopes on the basis of the simple shell-model plus pairing forces.