Energy Levels inPb206from the Decay ofBi206

The energies, spins, and parities of 10 excited states in ${\mathrm{Pb}}^{206}$ and the probable energies, spins, and parities of two additional states have been established by studies of 6.4-day ${\mathrm{Bi}}^{206}$ decay. The experiments include—intensity and precision energy measurements on the conversion lines in a double-focusing spectrometer; coincidences between pairs of $K$-conversion lines in a two-lens "spectrogoniometer"; coincidences between gamma rays and conversion electrons in a modified intermediate-image spectrometer; discovery of a 145±15 microsecond isomeric state decaying by either of two $E3\mathrm{}$ transitions; examination of the low-energy conversion spectrum; and relative gamma intensity measurements with a scintillation spectrometer. The adopted decay scheme contains 28 of the observed transitions and satisfies all of the conditions imposed by the energy and coincidence measurements. A few additional very weak transitions are unassigned. It is shown from a theoretical analysis based on the shell model that the observed levels are in agreement with the approximate calculations. Eleven gamma rays decaying with a half-life of 14 days are assigned to ${\mathrm{Bi}}^{205}$.