It was demonstrated that the previously reported 1.8-hr ${\mathrm{Ce}}^{145}$ and 4.5-hr ${\mathrm{Pr}}^{145}$ do not occur among the uranium fission products. ${\mathrm{Ce}}^{146}$ and ${\mathrm{Pr}}^{146}$ were briefly reinvestigated: the former decays with a half-life of 13.9±0.6 minutes and emits $\beta$-rays of 0.9-Mev maximum energy followed by soft $\gamma$-rays; the latter decays with a half-life of 24.4±0.5 minutes and its maximum $\beta$-ray energy is 3.8 Mev. In addition, it was shown that any undiscovered short-lived Ce fission products must decay with half-lives shorter than 6 minutes.

• Received 25 November 1952

DOI:https://doi.org/10.1103/PhysRev.89.1267