Decay ofTl199andAu199

The decays of ${\mathrm{Tl}}^{199}$ to ${\mathrm{Hg}}^{199}$ and ${\mathrm{Au}}^{199}$ to ${\mathrm{Hg}}^{199}$ have been examined using gamma-ray coincidence spectrometry and angular correlation techniques. The level order as well as level spins of ${\mathrm{Hg}}^{199}$ deduced from this study support the recent work of Jung and Svedberg. The branching ratios of the electron capture transitions from ${\mathrm{Tl}}^{199}$ to six levels in ${\mathrm{Hg}}^{199}$ have also been determined. Particular emphasis was placed on obtaining the empirical parameters of importance to the measurement of the magnetic moment of the 158-keV first excited state in ${\mathrm{Hg}}^{199}$ as well as to the interpretation of the state as one member of a doublet resulting from coupling the $\frac{1}{2^{-}}$ ground state with the $2^{+}$ core excitation. This interpretation, due to de-Shalit, implies the interrelations of some of the magnetic moments and lifetimes of the states involved. This study supports such an interpretation.