Gamma Rays in Coincidence withKX Rays from the La, Ce, and Pr Fission Fragments ofCf252

An experiment has been carried out to study the $\gamma$ rays from the fission fragments of ${\mathrm{Cf}}^{252}$. The $Z$ values of the fragments studied were determined by detecting their $K{\alpha }_1$ x rays with a Si(Li) x-ray speectrometer. A single-channel analyzer was used to accept only pulses corresponding to the $K{\alpha }_1$ x rays of the element under study. The $\gamma$ rays were detected with a Ge(Li) detector, and a time coincidence system was used to accept only the $\gamma$-ray pulses that occurred within 0.175 μsec of the preselected x ray. Energy transitions in three fission elements, $\mathrm{La}\mathrm{}(Z=57\mathrm{})\mathrm{}$, $\mathrm{Ce}\mathrm{}(Z=58\mathrm{})\mathrm{}$, and $\mathrm{Pr}\mathrm{}(Z=59\mathrm{})\mathrm{}$, were observed in an energy range 125-300 keV. Eleven $\gamma$ transitions were seen in La, fourteen in Ce, and four in Pr, although some of the weaker $\gamma$ rays attributed to La and Pr may belong to $\mathrm{Ba}\mathrm{}(Z=56\mathrm{})\mathrm{}$ and $\mathrm{Nd}\mathrm{}(Z=60\mathrm{})\mathrm{}$, respectively.