Isomeric Level inPb205Formed in the Decay ofBi205

An activity of 4.8-msec half-life which is assigned to ${\mathrm{Pb}}^{205m}$ has been observed in the electron capture decay of 14.5-day ${\mathrm{Bi}}^{205}$. This isomeric level decays with the emission of 987.8, 703.3, and 284.4-kev gamma rays with relative transition intensities of 100, 10, and 10. No other gamma rays of energy greater than 10 kev were observed in the decay of this isomer. The 284.4- and 703.3-kev gamma rays are in coincidence but neither is in coincidence with the 987.8-kev transition. This evidence suggests that the 987.8-kev level de-excites directly to the ground state by the emission of a 284.4, 703.3 kev cascade with a 987.8-kev crossover. There is some evidence (not conclusive) that the 987.8-kev level itself may not be isomeric but that it may be fed entirely by a highly converted low-energy transition (