We present results from new spectral prompt $$\gamma${}$-ray measurements from the spontaneous fission of ${}^{252}$Cf. Apart from one recent experiment, about four decades have passed since the last dedicated experiments were reported in the literature. Hence, there was a need for a revision. We have measured prompt fission $$\gamma${}$ rays with both cerium-doped LaBr${}_{3}$ and CeBr${}_{3}$ scintillation detectors, both of which exhibit excellent timing and good energy resolution. The emission yield was determined to be ${$\nu${}}_{$\gamma${}}=(8.30\ifmmode\pm\else\textpm\fi{}0.08)$/fission and ${$\nu${}}_{$\gamma${}}=(8.31\ifmmode\pm\else\textpm\fi{}0.10)$/fission, with the average energy of ${$\epsilon${}}_{$\gamma${}}=(0.80\ifmmode\pm\else\textpm\fi{}0.01)$ MeV and ${$\epsilon${}}_{$\gamma${}}=(0.80\ifmmode\pm\else\textpm\fi{}0.01)$ MeV and total energy of ${E}_{$\gamma${},\mathrm{tot}}=(6.64\ifmmode\pm\else\textpm\fi{}0.08)$ MeV and ${E}_{$\gamma${},\mathrm{tot}}=(6.65\ifmmode\pm\else\textpm\fi{}0.12)$ MeV, with the LaBr${}_{3}$ and CeBr${}_{3}$ detectors, respectively. Since the results from the two detectors are in excellent agreement and confirm the historical data, but not those in the present evaluated nuclear data files, we strongly recommend an update.

In this paper we present results from measurements of prompt $$\gamma${}$ rays from the thermal neutron induced fission of ${}^{235}$U. Photons were measured in coincidence with fission fragments with cerium-doped LaCl${}_{3}$ and LaBr${}_{3}$ as well as CeBr${}_{3}$ scintillation detectors, which offer an intriguing combination of excellent timing resolution and good resolving power. The spectra measured with all employed detectors are in excellent agreement with respect to their shapes. Characteristic parameters were extracted for a $$\gamma${}$-energy range from 0.1 to 6.0 MeV and the results obtained with several detectors were averaged. From that, the average emission yield of prompt-fission $$\gamma${}$ rays was determined to be ${\overline{$\nu${}}}_{$\gamma${}}=(8.19\ifmmode\pm\else\textpm\fi{}0.11)$ per fission, the average energy per photon to be ${$\epsilon${}}_{$\gamma${}}=(0.85\ifmmode\pm\else\textpm\fi{}0.02)$ MeV, and the total energy to be ${E}_{$\gamma${},\mathrm{tot}}=(6.92\ifmmode\pm\else\textpm\fi{}0.09)$ MeV. The uncertainties are much lower than the 7.5$%$ requested for the modeling of advanced nuclear reactor cores. Estimating the influence of $$\gamma${}$ rays with energies between 6 and 10 MeV on the values determined in this work revealed a negligible deviation of the order of the found uncertainties.

In this paper we report on a new study of prompt $\gamma$-rays from the spontaneous fission of ${}^{252}\mathrm{Cf}$. Photons were measured in coincidence with fission fragments by employing four different lanthanide halide scintillation detectors. Together with results from a previous work of ours, we determined characteristic parameters with high precision, such as the average $\gamma$-ray multiplicity ${\overline{\nu }}_{\gamma }=(8.29\pm 0.13)$, the average energy per photon ${\epsilon }_{\gamma }=(0.80\pm 0.02)$ MeV, and the total $\gamma$-ray energy release per fission $E_{\gamma ,\text{tot}}=(6.65\pm 0.10)$ MeV. The excellent agreement between the individual results obtained in all six measurements proves the good repeatability of the applied experimental technique. The impact of low-energy photons, i.e., below 500 keV, on prompt fission $\gamma$-ray spectra characteristics has been investigated as well by comparing our results with those taken with the DANCE detector system, which appears to suffer from absorption effects in the low-energy region. Correction factors for this effect were estimated, giving results comparable to ours as well as to historical ones. From this we demonstrate that the different techniques of determining the average $\gamma$-ray multiplicity, either from a properly measured and normalized spectrum or a measured multiplicity distribution, give equivalent and consistent results.

In this paper we present results from the first high-precision prompt-$\gamma$-ray spectral measurements from the reaction ${}^{241}\mathrm{Pu}$($n_{\mathrm{th}}$, $f$). Apart from one recent experiment, no data are reported in the literature for this fissioning system, which motivated a new dedicated experiment. We have measured prompt-fission $\gamma$ rays with three cerium-doped $\mathrm{La}{\mathrm{Br}}_3$ (two $5.08\text{cm}\times 5.08$ cm and one $7.62\text{cm}\times 7.62$ cm) and one $\mathrm{Ce}{\mathrm{Br}}_3$ ($5.08\text{cm}\times 5.08$ cm) scintillation detectors, which all exhibit excellent timing and good energy resolution. The average $\gamma$-ray multiplicity was determined to be ${\overline{\nu }}_{\gamma }=(8.21\pm 0.09)$ per fission, the average energy to be ${\epsilon }_{\gamma }=(0.78\pm 0.01)$ MeV, and the total energy to be $E_{\gamma ,\text{tot}}=(6.41\pm 0.06)$ MeV as the weighted average from all detectors. Since the results from all detectors are in excellent agreement, and the total released $\gamma$ energy is modestly higher than the one in the present evaluated nuclear data files, we suspect that the underestimation of the prompt-$\gamma$ heating in nuclear reactors is due to fast-neutron-induced fission on ${}^{238}\mathrm{U}$ or rather from fission induced by $\gamma$ rays from neutron capture in the construction material.

In this paper we present new results for prompt fission $\gamma$-ray spectral characteristics from the thermal neutron induced fission of ${}^{240}\mathrm{Pu}^{*}$. The measured spectra were unfolded by using the detectors' response functions, simulated with geant4. We obtained in average per fission a $\gamma$-ray multiplicity ${\overline{M}}_{\gamma }=(7.35\pm 0.12)$, a mean photon energy ${\overline{\epsilon }}_{\gamma }=(0.85\pm 0.02)$ MeV, and an average total energy released in fission ${\overline{E}}_{\gamma ,\mathrm{tot}}=(6.27\pm 0.11)$ MeV. Our results are in good agreement with historical data measured in the 1970s by Verbinski et al. and results from recent calculations in the framework of Monte Carlo Hauser–Feshbach models. Our measured average total energy is slightly smaller than the one deduced previously and present in evaluated data. From this we conclude that the ${}^{239}\mathrm{Pu}(n_{\mathrm{th}},f)$ reaction may be ruled out as possible source of $\gamma$ heating underestimation, when compared with benchmark calculations based on existing nuclear data.