The radiations of ${\mathrm{Ce}}^{146}$ and ${\mathrm{Pr}}^{146}$ fission products were investigated with a scintillation coincidence spectrometer. The 24.4-min ${\mathrm{Pr}}^{146}$ was shown to decay by two $\beta$ branches of maximum energy 2.3±0.2 Mev and 3.7±0.2 Mev and of about equal intensity. Gamma rays of 455±13 kev, 750±30 kev, and 1490±40 kev were observed; the 455-kev $\gamma$ ray was the most intense, and the 750-kev line was shown to consist of two $\gamma$ rays of about the same energy. A probable decay scheme is given. The 13.9-min ${\mathrm{Ce}}^{146}$ was found to emit $\beta$ rays of 700±100 kev maximum energy in coincidence with all of the $\gamma$ rays. Abundant $\gamma$ rays of 110±5 kev, 142±5 kev, 220±10 kev, 320±10 kev, and weak $\gamma$ rays of about 50 kev, about 250 kev, and 270±10 kev were observed. The relative intensities and the observed $\gamma -\gamma$ coincidences are tabulated, but the data were insufficient to determine a unique decay scheme. Some of the $\gamma$ rays were partially internally converted giving rise to Pr $K$ x-rays.

• Received 24 November 1953

DOI:https://doi.org/10.1103/PhysRev.93.1073