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The gamma-ray emissions from a radiopure cerium-bromide crystal with a mass of 4381 g were measured for a total of 497.4 d by means of high-resolution gamma-ray spectrometry in the HADES underground laboratory at a depth of 500 m.w.e. A search for 0/2nee and 0/2neb+ double beta decay transitions of Ce-136 and Ce-138 was performed using Bayesian analysis techniques. No signals were observed for a total of 35 investigated decay modes. 90% credibility limits were set in the order of 1e18-1e19 a. Existing constraints from a cerium oxide powder measurement were tested with a different cerium compound and half-life limits could be improved for most of the decay modes. The most likely accessible decay mode of the Ce-136 2nee transition into the 0+1 state of Ba-136 results in a new best 90% credibility limit of 5.0e18 a.

Monte-Carlo simulations to calculate the number of prompt particles emitted during fission were performed using the FIFRELIN code and compared to recent experimental data. We show that we are able to reproduce both the neutron and gamma-ray multiplicity distributions as a function of the pre-neutron mass of the fission fragments using a single consistent set of parameters. This result was made possible by using an energy-dependent spin cut-off model, driving the initial total angular momentum of the fission fragments, together with microscopic level densities from the HFB plus combinatorial method. We also discuss, how the initial excitation-energy sharing shapes the TKE-dependent gamma-ray multiplicity.(c) 2022 French Alternative Energies and Atomic Energy Commission (CEA). Published by Elsevier B.V.This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP3.

The VElocity foR Direct particle Identification spectrometer (VERDI) is a 2E-2v fission spectrometer that allows the measurement of the total mass distribution of secondary fission fragments with a resolving power of 1-2 u. It consists of two time-of-flight (ToF) arms, with one Micro Channel Plate (MCP) detector and up to 32 Silicon PIPS (Passive Implanted Planar Silicon) detectors per arm. The MCPs provide the start timing signals and the PIPS detectors provide both the energy and the stopping ToF signals. In real conditions, the PIPS signals are affected by the formation of plasma from the interaction between the heavy ions and the detector material. The plasma contributes to a reduction in signal amplitude, resulting in a Pulse Height Defect (PHD), and introduces a signal delay, known as Plasma Delay Time (PDT). An experiment to characterize the PDT and PHD was performed at the LOHENGRIN recoil separator of the Institut Laue Langevin (ILL). Characteristic fission fragments from the 239Pu(n,f) reaction were separated based on their A/Q and E/Q ratios, allowing the measurement of a wide range of energies from 21 to 110 MeV and masses between 80 and 149 u. Six PIPS detectors were characterized to study their individual responses to the PDT and PHD effects. The signals were recorded in a digital acquisition system to completely exploit the offline analysis capabilities. Achieved combined timing and energy resolutions for fission fragments varied between 72(2) ps and 100(4) ps and 1.4% - 2% (FWHM), respectively. Preliminary PHD and PDT data are presented from the masses A=85, 95, 130 and 143. The PHD trends are strongly correlated with both the ion energy and mass. The PDT, on the other hand, shows a strong variation as a function of the ion kinetic energy but a smaller dependence on the ion mass.

The FIFRELIN Monte Carlo code has been upgraded recently by adding new capabilities, additional models and updated databases. Several examples are presented in this work as well as three different applications related to the prompt component in fission, gamma cascades from thermal neutron capture and the delayed component in fission associated to the time evolution of decay heat.

In this work we have reexamined the shape isomer in $^{235}\mathrm{U}$. Reanalyzing data from a previous experiment gave a half-life of ${T}_{1/2}=(11\ifmmode\pm\else\textpm\fi{}3)\phantom{\rule{4pt}{0ex}}\mathrm{ms}$ and a cross section for populating the isomer of ${\ensuremath{\sigma}}_{\mathrm{iso}}=(12\ifmmode\pm\else\textpm\fi{}1)\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{b}$. Combining these new results with measured properties of fission fragments from the reaction $^{234}\mathrm{U}(n,f)$ allowed extracting parameters describing the outer fission barrier. The deduced barrier parameters are ${E}_{B}=(5.7\ifmmode\pm\else\textpm\fi{}0.6)$ MeV and $\ensuremath{\hbar}{\ensuremath{\omega}}_{B}=(0.5\ifmmode\pm\else\textpm\fi{}0.1)$ MeV for the height and curvature, respectively, as well as the energy of the superdeformed ground state ${E}_{II}=(2.4\ifmmode\pm\else\textpm\fi{}0.6)$ MeV. Separate barrier parameters for the standard-1 and standard-2 fission modes have been estimated, too. Finally, the results obtained in this work have been successfully tested for their plausibility.

MONNET is a fast-neutron source based on a 3.5 MV tandem accelerator, located at the Geel (BE) site of the Joint esearch Centre. It became operational in 2020. MONNET may deliver intense neutron beams in the energy range from 30 keV to 10.1 MeV and from 12.8 MeV to 24 MeV. Neutrons are generated by means of nuclear reactions in the target material (e.g. protons or deuterons on lithium-7, tritium or deuterium targets). MONNET delivers a neutron flux of up to 109 n/sr/s, depending on the producing reaction and the neutron energy. Neutron beams are essentially mono-energetic (∆En/En < 6% with En > 300 keV). The accelerator may also be used with proton and deuteron beams. Alpha beams will be offered soon. Photon beams are possible and presently under investigation. The research program ranges from cross section measurements, e.g. (n, f), (n, p), (n, α) as well as (p, p′), (p, n) and (p, γ), nuclear fission research, material studies (e.g. radiation-induced damage), to the investigation of advanced methods in nuclear technologies, safety and security. The MONNET neutron source offers beamtime to external user within the JRC EUFRAT Open Access program. Proposal evaluation by an independent panel is taking place up to two times per year.

Prompt fission $\ensuremath{\gamma}$ rays (PFGs) resulting from the $^{240}\mathrm{Pu}(d,p\mathrm{f})$ reaction have been measured as a function of fissioning nucleus excitation energy ${E}_{\text{x}}$ at the Oslo Cyclotron Laboratory. We study the average total PFG multiplicity per fission, the average total PFG energy released per fission, and the average PFG energy. No significant changes in these characteristics are observed over the range $5.75l{E}_{\text{x}}l8.25$ MeV. The physical implications of this result are discussed. The experimental results are compared to simulations conducted using the computational fission model FREYA. We find that FREYA reproduces the experimental PFG characteristics within $8%$ deviation across the ${E}_{\text{x}}$ range studied. Previous excitation energy-dependent PFG measurements conducted below the second-chance fission threshold have large uncertainties, but are generally in agreement with our results within a $2\ensuremath{\sigma}$ confidence interval. However, both a published parametrization of the PFG energy dependence and the most recent PFG evaluation included in ENDF/B-VIII.0 were found to poorly describe the PFG excitation-energy dependence observed in this and previous experiments.

The cross-section function for the $$^{115}$$ In( $$\gamma $$ , $$\gamma ^{\prime }$$ ) $$^{115m}$$ In reaction was determined in the energy range up to E $$_\gamma $$ = 9.6 MeV using the bremsstrahlung facility at the MT25 Microtron, JINR, Dubna. Natural indium disks were irradiated with bremsstrahlung, each disk with a beam of different endpoint energy. To the measured saturation activity built up in the wide-energy photon beam we applied the unfolding technique, developed recently at the JRC-Geel with the primary purpose of being used in neutron activation. The results were compared with TALYS 1.9 calculations and existing experimental data. Our results suggest that the application of existing unfolding technique allow determining unknown excitation functions of photon-induced reactions.

In response to nuclear data requests by OECD NEA, we present here the first results with respect to prompt-fission $$\gamma $$ -ray spectra characteristics for fast neutrons on $$^{235}$$ U. For that we have analyzed previously taken prompt-fission $$\gamma $$ -ray data from the reaction $$^{235}$$ U(n, f) induced by fast neutrons of average energy $${\overline{E}}_{n}$$ = 1.7 MeV and spectral properties were deduced. It was expected that the values would be somewhat higher than for thermal-neutron induced fission of the same system, which at a first glance turned out to be not the case. However, taking the different prompt time windows relative to the coincidence timing resolution between both measurements into account, this discrepancy could be resolved. The results are an average multiplicity $${\overline{M}}_{\gamma }$$ = 7.45 ± 0.48 $$\gamma $$ rays per fission and an average total $$\gamma $$ -ray energy release in fission $${\overline{E}}_{\gamma ,tot}$$ = (6.03 ± 0.47) MeV, which includes an additional relative uncertainty of 4% from the time window correction. The corresponding average energy per $$\gamma $$ ray is $${\overline{\epsilon }}_{\gamma }$$ = (0.81 ± 0.04) MeV.

The time dependence of prompt $$\gamma $$ -ray spectral characteristics, in particular the multiplicity, was studied during the first 10 ns after the spontaneous fission of $${}^{252}$$ Cf. The impact of prompt window and experimental time resolution on the determination of prompt multiplicities is assessed and described mathematically. As a consequence we are able to offer corrections that allow a reliable comparison of results from different measurements. An apparent discrepancy between a theoretical and an experimentally found time dependence is explained by the influence of a finite experimental timing resolution as well as the choice of the prompt timing window.

In recent years nuclear fission has gained renewed interest both from the nuclear energy community and in basic science. The first, represented by the OECD Nuclear Energy Agency, expressed the need for more accurate fission cross-section and fragment yield data for safety assessments of Generation IV reactor systems. In basic science modelling made much progress in describing the de-excitation mechanism of neutron-rich isotopes, e.g. produced in nuclear fission. Benchmarking the different models require a precise experimental data on prompt fission neutron and γ -ray emission, e.g. multiplicity, average energy per particle and total dissipated energy per fission, preferably as function of fission-fragment mass and total kinetic energy. A collaboration of scientists from JRC Geel (formerly known as JRC IRMM) and other institutes took the lead in establishing a dedicated measurement programme on prompt fission neutron and γ -ray characteristics, which has triggered even more measurement activities around the world. This contribution presents new advanced instrumentation and methodology we use to generate high-precision spectral data and will give a flavour of future data needs and opportunities.

For the detection of energetic charged particles, gaseous ionization detectors use a variety of counting gases. We studied the properties of non-flammable, high stopping-power Ar + CF 4 as counting gas. We assess the usability of different mixtures for compact, high-luminosity fast ionization chambers for future applications in nuclear photonics . The pulse-height defect (PHD) of Ar + CF 4 mixtures at different pressures has been extracted in comparison to P-10 gas (90%Ar + 10%CH 4 ) for fragments from 252Cf spontaneous fission in a twin Frisch-grid ionization chamber. For the different mixtures of Ar + CF 4 (P-10), a PHD of 4.5–11 MeV (4 MeV) and 6–12 MeV (5.5 MeV) for light and heavy fragments, respectively, have been measured. Based on these findings, reconstructed 252Cf mass and total kinetic energy distributions are consistent with literature, which demonstrates success in the PHD correction procedure.

We report on spectroscopic information and lifetime measurements of even-even neutron-rich Te isotopes. Excited states were populated in fast-neutron induced fission of U238 at the ALTO facility of IJCLab with the LICORNE neutron source and detected using the hybrid ν-ball spectrometer. We provide first results on lifetimes of the 61+ state in Te136 and the (61+), (41+), and (21+) states in Te138 and discuss the results in the context of large-scale shell-model calculations. The level schemes of Te136 and Te138 are revised in terms of lifetimes of their 21+,41+ states and updated information on the (42+) state in Te136 is presented. In addition, previously reported data on spectroscopy and lifetimes in Te134 are reexamined. This work provides new insights into the evolution of collectivity for Te isotopes with N=82,84,86.

We report on spectroscopic information and lifetime measurements of even-even neutron-rich Te isotopes. Excited states were populated in fast-neutron induced fission of 238U at the ALTO facility of IJCLab with the LICORNE neutron source and detected using the hybrid ν-ball spectrometer. We provide first results on lifetimes of the 6+1 state in 136Te and the (6+1), (4+1), and (2+1) states in 138Te and discuss the results in the context of large-scale shell-model calculations. The level schemes of 136Te and 138Te are revised in terms of lifetimes of their 2+1,4+1 states and updated information on the (4+2) state in 136Te is presented. In addition, previously reported data on spectroscopy and lifetimes in 134Te are reexamined. This work provides new insights into the evolution of collectivity for Te isotopes with N=82,84,86.

Prompt and delayed γ -ray spectroscopy of the neutron-rich 94 Kr was performed, as part of the fission campaign at the ALTO facility of the IPN Orsay, using the fast-neutron-induced fission reaction 238 U ( n , f ) in combination with the ν -Ball array, a novel hybrid γ spectrometer for energy and lifetime measurements. Several new yrast and nonyrast transitions were observed for the first time, extending the previously known level scheme. Additionally, we report on the observation of a new short-lived isomer at 3444 keV with a half-life of 32(3) ns. The analysis of the Nilsson orbitals obtained from Gogny cranked Hartree-Fock-Bogoliubov calculations suggests a ( 9 − ) spin and an oblate deformation for this isomer corresponding to a two-quasineutron state, indicating an isomeric structure very similar to that of the neighboring isotones 96 Sr and 92 Se

Background: The sharing of excitation energy between the fission fragments is one of the key issues in studying nuclear fission. One way to address this is by studying prompt-fission neutron multiplicities as a function of other fission observables such as the mass, $\overline{\ensuremath{\nu}}\left(A\right)$. These are vital benchmark data for both fission and nuclear deexcitation models, putting constrains on the fragment excitation energy and hence on the competing prompt neutron/$\ensuremath{\gamma}$-ray emission. Despite numerous detailed studies, recent measurements done at JRC-Geel with the SCINTIA array in the epithermal region show surprisingly strong discrepancies to earlier thermal fission data and the Wahl systematics.Purpose: The purpose was to perform measurements of the prompt-fission neutron multiplicity, as a function of fragment mass and total kinetic energy (TKE), in $^{235}\mathrm{U}\left({\text{n}}_{\text{th}},\text{f}\right)$ and $^{252}\mathrm{Cf}\left(\text{sf}\right)$, to verify and extend the SCINTIA results. Another goal was to validate the analysis methods, and prepare for planned investigations at excitation energies up to 5.5 MeV.Methods: The experiments were conducted at the former 7 MV Van de Graaff facility in JRC-Geel, using a Twin Frisch-Grid Ionization Chamber and two liquid scintillation detectors. A neutron beam with an average energy of 0.5 MeV was produced via the $^{7}\mathrm{Li}$(p,n) reaction. The neutrons were thermalized by a 12 cm thick block of paraffin. Digital data acquisition systems were utilized. Comprehensive simulations were performed to verify the methodology and to investigate the role of the mass and energy resolution on measured $\overline{\ensuremath{\nu}}\left(A\right)$ and $\overline{\ensuremath{\nu}}\left(\text{TKE}\right)$ values. The simulation results also revealed that the $\ensuremath{\partial}\overline{\ensuremath{\nu}}(A)/\ensuremath{\partial}A$ and $\ensuremath{\partial}\overline{\text{TKE}}/\ensuremath{\partial}\overline{\ensuremath{\nu}}$ are affected by the mass and energy resolution. However, the effect is small for the estimated resolutions of this work. Detailed Fluka simulations were performed to calculate the fraction of thermal neutron-induced fission, which was estimated to be about $98%$.Results: The experimental results on $\overline{\ensuremath{\nu}}\left(A\right)$ are in good agreement with earlier data for $^{252}\mathrm{Cf}\left(\text{sf}\right)$. For $^{235}\mathrm{U}\left({\text{n}}_{\text{th}},\text{f}\right)$, the $\overline{\ensuremath{\nu}}\left(A\right)$ data is very similar to the data obtained with SCINTIA, and therefore we verify these disclosed discrepancies to earlier thermal data and to the Wahl evaluation. The experimental results on $\overline{\ensuremath{\nu}}\left(\text{TKE}\right)$ are also in agreement with the data at epithermal energies. For $^{252}\mathrm{Cf}\left(\text{sf}\right)$ a slope value of $\ensuremath{\partial}\overline{\text{TKE}}/\ensuremath{\partial}\overline{\ensuremath{\nu}}=\left(\ensuremath{-}12.9\ifmmode\pm\else\textpm\fi{}0.2\right)\phantom{\rule{0.28em}{0ex}}\mathrm{MeV}/\mathrm{n}$ was obtained. For $^{235}\mathrm{U}\left({\text{n}}_{\text{th}},\text{f}\right)$ the value is $\left(\ensuremath{-}12.0\ifmmode\pm\else\textpm\fi{}0.1\right)\phantom{\rule{0.28em}{0ex}}\mathrm{MeV}/\mathrm{n}$. Finally, the neutron spectrum in the center-of-mass system was derived and plotted as a function of fragment mass.Conclusions: This work clearly proves the lack of accurate correlation between fission fragment and neutron data even in the best-studied reactions. The new results highlight the need of a new evaluation of the prompt-fission multiplicity for $^{235}\mathrm{U}\left({\text{n}}_{\text{th}},\text{f}\right)$.

Prompt γ rays from the spontaneous fission of 252Cf were measured with cerium-doped LaBr3 detectors. The average prompt fission γ-ray multiplicity, M γ , was determined as a function of fragment mass number (A) and total kinetic energy (TKE). High-statistics data, obtained from three detectors of different size at different angles relative to the fission chamber, confirms unequivocally a saw-tooth like shape of the γ multiplicity as a function of fragment mass, in contrast to previously published data. In addition, the TKE-dependence of M γ was determined experimentally and compared with recent data.

The knowledge of prompt fission $\ensuremath{\gamma}$-ray emission has been of major interest in reactor physics for a few years. Only few experimental spectra were published until now for fast-neutron-induced fission, and measurements would be also valuable in order to improve our understanding of the fission process. A simple experimental method was used to measure the first prompt fission $\ensuremath{\gamma}$-ray spectra up to 10 MeV. In this approach, the $\ensuremath{\gamma}$ rays are measured with a bismuth germanate (BGO) detector which offers two significant advantages with respect to other $\ensuremath{\gamma}$-ray detectors: a high peak-to-total ratio and a high efficiency. The prompt fission neutrons are rejected by the time-of-flight technique between the BGO detector and a fission trigger given by a fission chamber. Prompt fission $\ensuremath{\gamma}$-ray spectra were measured for 1.6 \ifmmode\pm\else\textpm\fi{} 0.1, 5.1 \ifmmode\pm\else\textpm\fi{} 0.2 and 15.0 \ifmmode\pm\else\textpm\fi{} 0.6 MeV neutron-induced fission on $^{238}\mathrm{U}$ at the CEA, DAM, DIF Van de Graaff accelerator; average multiplicity and mean photon energy per fission were deduced from the spectra.

Using the NAXSUN technique developed at the JRC-Geel, the cross section functions for the neutron induced reactions $$^{187}$$ Re(n,p) $$^{187}$$ W and $$^{185}$$ Re(n,3n) $$^{183}$$ Re have been measured in the energy range between 13.08 MeV and 19.5 MeV. These data are the first experimentally obtained values for those nuclear reactions in this neutron energy range. Obtained results have been compared with existing evaluated data from ENDF/B-VII 0, JEFF 3.3, JEFF 3.2, BROND 3.1, JEF - 2.2, JENDL, ROSFO ND-2010, TENDL-2017, EAF-2010, FENDL-3.1c. The TALYS 1.9 and EMPIRE 3.2.3 calculations were performed using different available models and calculations using several semi-empirical existing formulas. A comparison between theoretical model calculations and experimental results was made.

We report on the measurement of lifetimes of excited states in the near-mid-shell nuclei Dy164,166 using the gamma-ray coincidence fast-timing method. The nuclei of interest were populated using reactions between an O18 beam and a gold-backed isotopically enriched Dy164 target of thickness 6.3mg/cm2 at primary beam energies of 71, 76, and 80 MeV from the IPN-Orsay laboratory, France. Excited states were populated in Dy164, Dy166, and W178,179 following Coulomb excitation, inelastic nuclear scattering, two-neutron transfer, and fusion-evaporation reaction channels respectively. Gamma rays from excited states were measured using the ν-Ball high-purity germanium (HPGe)-LaBr3 hybrid γ-ray spectrometer with the excited state lifetimes extracted using the fast-timing coincidence method using HPGe-gated LaBr3-LaBr3 triple coincident events. The lifetime of the first Iπ=2+ excited state in Dy166 was used to determine the transition quadrupole deformation of this neutron-rich nucleus for the first time. The experimental methodology was validated by showing consistency with previously determined excited state lifetimes in Dy164. The half-lives of the yrast 2+ states in Dy164 and Dy166 were 2.35(6) and 2.3(2) ns, respectively, corresponding to transition quadrupole moment values of Q0=7.58(9) and 7.5(4) eb, respectively. The lifetime of the yrast 2+ state in Dy166 is consistent with a quenching of nuclear quadrupole deformation at β≈0.35 as the N=104 mid-shell is approached.

Prompt and delayed γ-ray spectroscopy of the neutron-rich 94Kr was performed, as part of the fission campaign at the ALTO facility of the IPN Orsay, using the fast-neutron-induced fission reaction 238U(n,f) in combination with the ν-Ball array, a novel hybrid γ spectrometer for energy and lifetime measurements. Several new yrast and nonyrast transitions were observed for the first time, extending the previously known level scheme. Additionally, we report on the observation of a new short-lived isomer at 3444 keV with a half-life of 32(3) ns. The analysis of the Nilsson orbitals obtained from Gogny cranked Hartree-Fock-Bogoliubov calculations suggests a (9−) spin and an oblate deformation for this isomer corresponding to a two-quasineutron state, indicating an isomeric structure very similar to that of the neighboring isotones 96Sr and 92Se.

New active-interrogation nondestructive assay techniques are needed for safeguard purpose. They can be used for the quantification of the fissile composition in high radioactivity nuclear material samples. One of the techniques under evaluation by the Japan Atomic Energy Agency together with the European Commission Joint Research Centre is delayed gamma-ray spectroscopy. It utilizes a combination of high rate neutron sources and moderation to thermal energy to induce fission in the fissile nuclides. This will allow enhancing the amount of observable coming from the fission of the fissile compared with the fertile nuclides that are usually more abundant in the sample. Analyzing the peaks ratios of gamma-rays with energy above 3 MeV emitted by the short lived fission products produced in the sample, it is possible to verify the initial composition of the fissile nuclides. We are currently designing and testing several different systems with the goal to design a practical and compact system that can be installed in current reprocessing facilities. In particular, this paper describes the different systems currently tested focusing on the different neutron source and moderator material and geometry as well as different gamma-ray detectors. We will also show the new neutron and gamma-ray detector systems we will implement for future test and development.

Prompt-fission $\ensuremath{\gamma}$-ray spectra (PFGS) have been measured for the $^{238}\mathrm{U}(n,f$) reaction using fast neutrons produced by the LICORNE directional neutron source. Fission events were detected with an ionization chamber containing actinide samples placed in the neutron beam, and the coincident prompt-fission $\ensuremath{\gamma}$ rays were measured using a number of ${\mathrm{LaBr}}_{3}$ scintillation detectors and a cluster of nine phoswich detectors from the PARIS array. Prompt-fission $\ensuremath{\gamma}$ rays (PFGs) were discriminated from prompt-fission neutrons using the time-of-flight technique over distances of around 35 cm. PFG emission spectra were measured at two incident neutron energies of 1.9 and 4.8 MeV for $^{238}\mathrm{U}(n,f$) and also for $^{252}\mathrm{Cf}(sf$) as a reference. Spectral characteristics of PFG emission, such as mean $\ensuremath{\gamma}$ multiplicity and average total $\ensuremath{\gamma}$-ray energy per fission, as well as the average $\ensuremath{\gamma}$-ray energy, were extracted. The sensitivity of these results to the width of the time window and the type of spectral unfolding procedure used to correct for the detector responses was studied. Iteration methods were found to be more stable in low-statistics data sets. The measured values at ${E}_{n}=1.9\phantom{\rule{4.pt}{0ex}}\text{MeV}$ were found to be the mean $\ensuremath{\gamma}$ multiplicity ${\overline{M}}_{\ensuremath{\gamma}}=6.54\ifmmode\pm\else\textpm\fi{}0.19$, total released energy per fission ${E}_{\ensuremath{\gamma},\mathrm{tot}}=5.25\ifmmode\pm\else\textpm\fi{}0.20$ MeV, and the average $\ensuremath{\gamma}$-ray energy ${\ensuremath{\epsilon}}_{\ensuremath{\gamma}}=0.80\ifmmode\pm\else\textpm\fi{}0.04$ MeV. Under similar conditions, the values at ${E}_{n}=4.8\phantom{\rule{4.pt}{0ex}}\text{MeV}$ were measured to be ${\overline{M}}_{\ensuremath{\gamma}}=7.31\ifmmode\pm\else\textpm\fi{}0.46, {E}_{\ensuremath{\gamma},\mathrm{tot}}=6.18\ifmmode\pm\else\textpm\fi{}0.65$ MeV, and ${\ensuremath{\epsilon}}_{\ensuremath{\gamma}}=0.84\ifmmode\pm\else\textpm\fi{}0.11$ MeV.

Prompt fission gamma-ray spectra (PFGS) have been measured for the 239Pu(n,f) reaction using fast neutrons at Ēn=1.81 MeV produced by the LICORNE directional neutron source. The setup makes use of LaBr3 scintillation detectors and PARIS phoswich detectors to measure the emitted prompt fission gamma rays (PFG). The mean multiplicity, average total energy release per fission and average energy of photons are extracted from the unfolded PFGS. These new measurements provide complementary information to other recent work on thermal neutron induced fission of 239Pu and spontaneous fission of 252Cf.

The reaction of a pulsed 18O beam on a 164Dy target was studied in the first experiment with the NuBall array at the IPN Orsay, France. Excited state half-lives were measured using the fast timing method with 20 LaBr3(Ce) detectors. The timing characteristics of the fully digital acquisition system is briefly discussed. A value for the previously unknown half-life of the first excited 4+ state in 178W is presented.

Single-crystal chemical vapor-deposited diamond (sCVD) was investigated for its ability to act as fission-fragment detector. In particular we investigated timing and energy resolution for application in a simultaneous time-of-flight and energy measurement to determine the mass of the detected fission fragment. Previous tests have shown that poly-crystalline chemical vapor deposited (pCVD) diamonds provide sufficient timing resolution, but their poor energy resolution did not allow complete separation between very low-energy fission fragments, α-particles and noise. Our present investigations prove artificial sCVD diamonds to show similar timing resolution as pCVD diamonds close to 100ps. Improved pulse-height resolution allows the unequivocal separation of fission fragments, and the detection efficiency reaches 100%, but remains with about a few percent behind requirements for fragment-mass identification. With high-speed digital electronics a timing resolution well below 100ps is possible. However, the strongly varying quality of the presently available diamond material does not allow application on a sufficiently large scale within reasonable investments.

In this work we give an overview of our investigations of prompt gamma-ray emission in nuclear fission. This work was conducted during the last five years in response to a high priority nuclear data request formulated by the OECD/NEA. The aim was to reveal data deficiencies responsible for a severe under-prediction of the prompt gamma heating in nuclear reactor cores. We obtained new prompt fission gamma-ray spectral (PFGS) data for Cf-252(SF) as well as for thermal-neutron induced fission on U-235(nth,f) and Pu-241(nth,f). In addition, first PFGS measurements with a fast-neutron beam were accomplished, too. The impact of the new data and future data needs are discussed.

Prompt gamma-ray and neutron emission data in fission integrates a large amount of information on the fission process and can shed light on the partition of energy. Measured emission spectra, average energies and multiplicities also provide important information for energy applications. While current reactors mostly use thermal neutron spectra, the future reactors of Generation IV will use fast neutron spectra for which little experimental prompt emission data exist.Initial investigations on prompt emission in fast neutron induced fission have recently been carried out at the LICORNE facility at the IPN Orsay, which exploits inverse reactions to produce naturally collimated, intense beams of neutrons. We report on first results with LICORNE to measure prompt fission gamma-ray spectra, average energies and multiplicities for 235U and 238U. Current improvements and upgrades being carried out on the LICORNE facility will also be described, including the development of a H2 gas target to reduce parasitic backgrounds and increase intensities, and the deployment of 11B beams to extend the effective LICORNE neutron energy range up to 12 MeV. Prospects for future experimental studies of prompt gamma-ray and neutron emission in fast neutron induced fission will be presented.

The reaction of a pulsed 18O beam on a self-supporting and gold-backed isotopically-enriched 164Dy target of thickness 6.3 mg/cm2 at separate primary beam energies of 71, 76 and 80 MeV was studied at the accelerator at the ALTO facility of the IPN Orsay. The γ rays produced were detected using the newly-constructed ν-Ball spectrometer which comprised of HPGe and LaBr3(Ce) detectors. This conference paper describes the methodology and effectiveness of multiplicity/sum-energy gating, for channel selection between fusion evaporation events and lower multiplicity/energy events from inelastic nuclear scattering and Coulomb excitation of the target, and from two-neutron transfer reactions to 166Dy.

Author(s): Rose, SJ; Zeiser, F; Wilson, JN; Oberstedt, A; Oberstedt, S; Siem, S; Tveten, GM; Bernstein, LA; Bleuel, DL; Brown, JA; Crespo Campo, L; Giacoppo, F; Gorgen, A; Guttormsen, M; Hadynska, K; Hafreager, A; Hagen, TW; Klintefjord, M; Laplace, TA; Larsen, AC; Renstrom, T; Sahin, E; Schmitt, C; Tornyi, TG; Wiedeking, M | Abstract: Prompt-fission γ rays are responsible for approximately 5% of the total energy released in fission, and therefore important to understand when modeling nuclear reactors. In this work we present prompt γ-ray emission characteristics in fission as a function of the nuclear excitation energy of the fissioning system. Emitted γ-ray spectra were measured, and γ-ray multiplicities and average and total γ energies per fission were determined for the U(d,pf)233 reaction for excitation energies between 4.8 and 10 MeV, and for the Pu(d,pf)239 reaction between 4.5 and 9 MeV. The spectral characteristics show no significant change as a function of excitation energy above the fission barrier, despite the fact that an extra ∼5 MeV of energy is potentially available in the excited fragments for γ decay. The measured results are compared with model calculations made for prompt γ-ray emission with the fission model code gef. Further comparison with previously obtained results from thermal neutron induced fission is made to characterize possible differences arising from using the surrogate (d,p) reaction.

© 2017 American Physical Society. Prompt-fission γ rays are responsible for approximately 5% of the total energy released in fission, and therefore important to understand when modeling nuclear reactors. In this work we present prompt γ-ray emission characteristics in fission as a function of the nuclear excitation energy of the fissioning system. Emitted γ-ray spectra were measured, and γ-ray multiplicities and average and total γ energies per fission were determined for the U(d,pf)233 reaction for excitation energies between 4.8 and 10 MeV, and for the Pu(d,pf)239 reaction between 4.5 and 9 MeV. The spectral characteristics show no significant change as a function of excitation energy above the fission barrier, despite the fact that an extra ∼5 MeV of energy is potentially available in the excited fragments for γ decay. The measured results are compared with model calculations made for prompt γ-ray emission with the fission model code gef. Further comparison with previously obtained results from thermal neutron induced fission is made to characterize possible differences arising from using the surrogate (d,p) reaction.

Prompt-fission γ rays are responsible for approximately 5% of the total energy released in fission, and therefore important to understand when modeling nuclear reactors. In this work we present prompt γ-ray emission characteristics in fission as a function of the nuclear excitation energy of the fissioning system. Emitted γ-ray spectra were measured, and γ-ray multiplicities and average and total γ energies per fission were determined for the U(d,pf)233 reaction for excitation energies between 4.8 and 10 MeV, and for the Pu(d,pf)239 reaction between 4.5 and 9 MeV. The spectral characteristics show no significant change as a function of excitation energy above the fission barrier, despite the fact that an extra ∼5 MeV of energy is potentially available in the excited fragments for γ decay. The measured results are compared with model calculations made for prompt γ-ray emission with the fission model code gef. Further comparison with previously obtained results from thermal neutron induced fission is made to characterize possible differences arising from using the surrogate (d,p) reaction.

In this paper we present new results for prompt fission γ-ray spectral characteristics from the thermal neutron induced fission of Pu*240. The measured spectra were unfolded by using the detectors' response functions, simulated with geant4. We obtained in average per fission a γ-ray multiplicity M¯γ=(7.35±0.12), a mean photon energy e¯γ=(0.85±0.02) MeV, and an average total energy released in fission E¯γ,tot=(6.27±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 Pu239(nth,f) reaction may be ruled out as possible source of γ heating underestimation, when compared with benchmark calculations based on existing nuclear data.

Fast-neutron-induced fission of 238U at an energy just above the fission threshold is studied with a novel technique which involves the coupling of a high-efficiency γ-ray spectrometer (MINIBALL) to an inverse-kinematics neutron source (LICORNE) to extract charge yields of fission fragments via γ−γ coincidence spectroscopy. Experimental data and fission models are compared and found to be in reasonable agreement for many nuclei; however, significant discrepancies of up to 600% are observed, particularly for isotopes of Sn and Mo. This indicates that these models significantly overestimate the standard 1 fission mode and suggests that spherical shell effects in the nascent fission fragments are less important for low-energy fast-neutron-induced fission than for thermal neutron-induced fission. This has consequences for understanding and modeling the fission process, for experimental nuclear structure studies of the most neutron-rich nuclei, for future energy applications (e.g., Generation IV reactors which use fast-neutron spectra), and for the reactor antineutrino anomaly.

Prompt-fission γ rays are responsible for approximately 5% of the total energy released in fission, and therefore important to understand when modeling nuclear reactors. In this work we present prompt γ -ray emission characteristics in fission as a function of the nuclear excitation energy of the fissioning system. Emitted γ -ray spectra were measured, and γ -ray multiplicities and average and total γ energies per fission were determined for the 233 U ( d , p f ) reaction for excitation energies between 4.8 and 10 MeV, and for the 239 Pu ( d , p f ) reaction between 4.5 and 9 MeV. The spectral characteristics show no significant change as a function of excitation energy above the fission barrier, despite the fact that an extra ∼ 5 MeV of energy is potentially available in the excited fragments for γ decay. The measured results are compared with model calculations made for prompt γ -ray emission with the fission model code gef. Further comparison with previously obtained results from thermal neutron induced fission is made to characterize possible differences arising from using the surrogate ( d , p ) reaction.

In this paper we present new results for prompt fission γ -ray spectral characteristics from the thermal neutron induced fission of 240 Pu ∗ . The measured spectra were unfolded by using the detectors' response functions, simulated with geant4. We obtained in average per fission a γ -ray multiplicity ¯¯¯¯ M γ = ( 7.35 ± 0.12 ) , a mean photon energy ¯ ε γ = ( 0.85 ± 0.02 ) MeV, and an average total energy released in fission ¯¯¯ E γ , tot = ( 6.27 ± 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 Pu ( n th , f ) reaction may be ruled out as possible source of γ heating underestimation, when compared with benchmark calculations based on existing nuclear data.

Recent experimental investigations on major and minor actinides at the JRC-IRMM are presented. Fission-fragment distributions of isotopes with vibrational resonances in the sub-threshold fission cross section, i. e. 234,238U, have been measured. For 234U, the impact of an increased neutron multiplicity for the heavy fragments with higher incident neutron energies has been studied as observed in experiment and also recently theoretically predicted. The impact is found to be noticeable on post-neutron mass yields, which are the relevant quantities for a-priori waste assessments. The fission cross sections for 240,242Pu at threshold and in the plateau region are being investigated within the ANDES project. The results show some discrepancies to the ENDF/B-VII.1 evaluation mainly for 242Pu around 1 MeV, where the evaluation exhibits a resonance-like structure not observed so clearly in the present work. The requested target accuracy in design studies of innovative reactor concepts like Gen-IV is in the range of a few percent. In order to be able to respond to requests for measurements of prompt neutron and γ-ray emission in fission JRC-IRMM has also invested in setting up a neutron and γ-ray detector array. The neutron array is called SCINTIA and has so far been tested with 252Cf(SF). For γ-ray multiplicity and spectrum measurements of 252Cf(SF) and 235U(nth, f) lanthanum- and cerium-halide detectors were successfully used., JRC.D.4-Standards for Nuclear Safety, Security and Safeguards

In this paper we report about new prompt fission gamma-ray measurements, which we have performed with highly efficient gamma-ray detectors based on lanthanide-halide crystals, aiming at very fast timing in conjunction with a good energy resolution. About four decades after the experiments were performed, whose results are still used for current evaluations, we present new spectral prompt fission gamma-ray data from the reactions Cf-252(SF) and U-235(n(th),f). Based on our new findings we recommend to replace the current ENDF/B-VII. 1 evaluation for Cf-252(SF) and U-235(n(th),f) as well as to perform new measurements for U-238(n,f) and Pu-241(n,f).

The bremstrahlung induced fission of 234,238U and 232Th has been studied at the superconducting Darmstadt linear accelerator (S- DALINAC) in the excitation energy region close to the fission barrier. In this contribution results on the fission fragment mass, total kinetic energy (TKE) and angular distributions will be presented. Fission fragment mass and TKE distributions from 234U were studied for the first time in this energy region. The results have been analyzed in terms of fission modes and a dominant yield of the mass asymmetric standard-2 mode was found in all studied nuclei. No strong dependence of the fission mode weights on the excitation energy of the compound nucleus were found. Correlations between mass, TKE and angular distributions have been investigated in 234U and 232Th. A correlation in form of an increased anisotropy for far-asymmetric masses and low TKE were found in both fissioning systems. A possible interpretation of this correlation in terms of fission modes is discussed.