The electron capture decay of ${}_{}{}^{199}{}_{}{}^{}\mathrm{Tl}$ to levels in ${}_{}{}^{199}{}_{}{}^{}\mathrm{Hg}$ has been reinvestigated. Twenty new transitions are assigned to the ${}_{}{}^{199}{}_{}{}^{}\mathrm{Tl}$ decay scheme and the population of two new levels in ${}_{}{}^{199}{}_{}{}^{}\mathrm{Hg}$ at 750.4 and 1221.2 keV is confirmed. A quasiparticle-phonon coupling model is applied to low-lying levels in ${}_{}{}^{199}{}_{}{}^{}\mathrm{Hg}$. Good agreement with experiment is obtained for the eigenvalues, spectroscopic factors, and electromagnetic transition rates and moments by variation of the $f_{\frac{5}{2}}$ neutron energy and by introducing a phenomenological reduction factor in the coupling matrix element.

RADIOACTIVITY ${}_{}{}^{199}{}_{}{}^{}\mathrm{Tl}$ measured $E_{\gamma }$, $I_{\gamma }$, $\gamma -\gamma$ coin, deduced $log\mathrm{ft}$. ${}_{}{}^{199}{}_{}{}^{}\mathrm{Hg}$ deduced levels, $J$, $\pi$.

NUCLEAR STRUCTURE ${}_{}{}^{199}{}_{}{}^{}\mathrm{Hg}$ calculated levels, $J$, $\pi$, $S$, $\mu$, $q$, $B\left(E2\mathrm{}\right)\mathrm{}$, $B\left(M1\mathrm{}\right)\mathrm{}$, $\delta$, branching ratios. Quasiparticle-phonon coupling.

• Received 4 November 1974

DOI:https://doi.org/10.1103/PhysRevC.11.587