New Prompt Fission γ-ray Spectral Data and its Implication on Present Evaluated Nuclear Data Files

In this paper we report on new spectral prompt γ-ray measurements from the spontaneous fission of 252Cf and thermal neutron- induced fission of 236U*. In both experiments, γ-ray multiplicities, average and total γ-energies were extracted. Apart from one recent measurement on 252Cf, about four decades have passed since the last dedicated experiments were reported in literature. Hence, there was a need for a revision, not only with respect to high priority nuclear data requests by the Nuclear Energy Agency (NEA). In the first mentioned experiment we have measured prompt fission γ-rays with both cerium-doped LaBr3 and CeBr3 scintillation detectors, which both exhibit excellent timing and good energy resolution. The results from both detectors are in excellent agreement with each other and confirm the historical data. In the experiment on 235U(nth,f) we employed cerium-doped LaCl3 detectors, together with the lanthanum bromide detectors mentioned above. Even here the first results indicate a good agreement with data from the early 1970's. They are also in accordance with data in evaluated libraries like ENDF/B-VII.0, while this is not the case for 252Cf(SF). Hence, here an update is strongly recommended.