Journal articles: 'Prompt Fission Neutrons'

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Lovell, A. E., P. Talou, I. Stetcu, and K. J. Kelly. "Anisotropy in fission fragment and prompt neutron angular distributions." EPJ Web of Conferences 256 (2021): 00009. http://dx.doi.org/10.1051/epjconf/202125600009.

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Several physics mechanisms can lead to the deviation from an isotropic angular distribution for both fission fragments and the neutrons that are emitted during the fission event. Two of these effects have recently been implemented into CGMF, the Monte Carlo fission event generator developed at Los Alamos National Laboratory: angular distribution sampling for fission fragments and pre-equilibrium neutrons (those emitted before the compound nucleus forms). Using these new developments, we show that the anisotropy of the neutrons reflects the anisotropy of the fission fragments, in particular as the outgoing energy of neutrons increases. Correlations between the fission fragment and neutron anisotropies could be used to extract the fission fragment anisotropy from the neutron angular distributions.

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Stanescu, Razvan, Hadrick Green, Toby Morris, Gencho Rusev, and Marian Jandel. "Prompt Fission Gamma-Ray Measurements at UML Research Reactor." EPJ Web of Conferences 242 (2020): 01009. http://dx.doi.org/10.1051/epjconf/202024201009.

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Neutron-induced fission of 235U was studied at the thermal column of the UMass Lowell 1 MW Research Reactor. A collimated, 2.25-inch diameter beam of thermal neutrons with the flux of ~5x105 n/cm2/sec induced fission reaction on a plate of low-enriched uranium with the areal density ~25 mg/cm2 of 235U. We have used the prompt fission-neutron tagging method to identify the fission reaction in the off-line analysis. The method employs the pulse-shape discrimination of neutrons and gamma-ray events in stilbene scintillator and enables identification of coincidence events of prompt fission gamma-rays and prompt fission neutrons in coincidence time intervals less than 20-30 ns. The prompt gamma-ray radiation was detected using two co-linear NaI(Tl) detectors. The measured spectra of prompt-fission gamma rays between 150 keV and 6 MeV are presented. The results from these initial measurements demonstrate the feasibility of the experimental method. Future measurements with extended arrays of detectors are planned.

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Kelly, Keegan J., Matthew Devlin, Jaime A. Gomez, John M. O’Donnell, Terry N. Taddeucci, Robert C. Haight, Hye Young Lee, et al. "Measurements of the Prompt Fission Neutron Spectrum at LANSCE: The Chi-Nu Experiment." EPJ Web of Conferences 193 (2018): 03003. http://dx.doi.org/10.1051/epjconf/201819303003.

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The goal of the Chi-Nu experiment at the Los Alamos Neutron Science Center is to measure the prompt fission neutron spectra from major actinides using a double time-of-flight method with a pulsed, white incoming neutron source. Fission events are detected with a parallel-plate avalanche counter and outgoing neutrons are detected with either a 6Li-glass or liquid scintillator detector array for low- or high-energy neutrons, respectively. A detector response matrix for the interaction of neutrons with the experimental environment for neutrons measured with the Chi-Nu 6Li-glass detector array has been calculated to obtain a full understanding of the measured Chi-Nu data and also to allow for nearly instantaneous production of simulated Chi-Nu data spectra. Prompt fission neutron spectra corresponding to 19 incoming neutron energy ranges from 0.7-20 MeV have been extracted using the ratio-of-ratios method with Chi-Nu 6Li-glass data on the neutron-induced fission of 235U.

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Lovell, A. E., T. Kawano, S. Okumura, M. R. Mumpower, I. Stetcu, and P. Talou. "The Extension of the Hauser-Feshbach Fission Fragment Decay Model to Multi-chance Fission and its Application to ²³⁹Pu." EPJ Web of Conferences 284 (2023): 04015. http://dx.doi.org/10.1051/epjconf/202328404015.

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The Hauser-Feshbach fission fragment decay model, HF3D, calculates the statistical decay of fission fragments through both prompt and delayed neutron and γ-ray emissions in a deterministic manner. While previously limited to the calculation of only first-chance fission, the model has recently been extended to include multi-chance fission, up to neutron incident energies of 20 MeV. The deterministic decay takes as input prescission quantities–fission probabilities, pre-fission neutron energies, and the average energy causing fission– and post-scission quantities–yields in mass, charge, total kinetic energy, spin, and parity. From those fission fragment initial conditions, the full decay is followed through both prompt and delayed particle emissions. The evaporation of the prompt neutrons and γ rays is calculated through the Hauser-Feshbach statistical theory, taking into account the competition between neutron and γ-ray emission, conserving energy, spin, and parity. The delayed emission is taken into account using time-independent calculation using decay data. This whole formulation allows for the calculation of prompt neutron and γ-ray properties, such as multiplicities and energy distributions, both independent and cumulative fission yields, and delayed neutron observables, in a consistent framework. Here, we describe the implementation of multi-chance fission into the HF3D model, and show an example of prompt and delayed quantities beyond first-chance fission, using the example of neutron-induced fission on 239Pu. This expansion represents significant progress in consistently modeling the emission of prompt and delayed particles from fissile systems.

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Devlin, Matthew, Jaime A. Gomez, Keegan J. Kelly, John M. O'Donnell, Robert C. Haight, Terry N. Taddeucci, Denise Neudecker, et al. "Prompt Fission Neutron Spectra for Neutron-Induced Fission of 239Pu and 235U." EPJ Web of Conferences 239 (2020): 01003. http://dx.doi.org/10.1051/epjconf/202023901003.

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We report the current results of a large effort to accurately measure the Prompt Fission Neutron Spectra (PFNS) for neutron-induced fission of 235U and 239Pu for incident neutrons with energies from 1 to 20 MeV. The Chi-Nu experiment at the Los Alamos Neutron Science Center used an unmoderated, white spectrum of neutrons to induce fission in actinide samples that were placed inside a parallel plate avalanche counter to provide a fast fission signal. A double time-of-flight technique was used to determine the incoming and outgoing neutron energies. Two neutron detector arrays, one with 54 liquid scintillators and another with 22 lithium glass detectors, were used to detect the outgoing neutrons and measure the PFNS distributions over a wide range in outgoing neutron energy, from below 100 keV to 10 MeV. Extensive Monte Carlo modeling was used to understand the experiment response and extract the PFNS. Systematic errors and uncertainties in the method have been examined and quantified. A summary of these results for incoming energies from 1 to 5 MeV is presented here.

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Oprea, Cristiana, Alexandru Mihul, and Alexandru Oprea. "Advanced Modelling of 238U(n,f) in a Fast Reactor Application." EPJ Web of Conferences 211 (2019): 04008. http://dx.doi.org/10.1051/epjconf/201921104008.

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Fast neutron reactors, as a possible future solution on energy demand of human society, based on fission process of 238U, request new and reliable nuclear data necessary for new generation reactors design. Fission process induced by fast neutrons on 238U was investigated. Fission observables like cross sections and their uncertainties, fission fragment mass distribution, prompt neutrons emission, isomer ratios and other parameters were obtained by using Talys computer code or programs realized by authors. Then the production of isotopes like 135,133Xe, 99Mo, 131I, 89Y as well as yields of fissile nuclei were evaluated. Obtained theoretical evaluations are compared with existing experimental data.

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Fujio, Kazuki, Ali Al-Adili, Fredrik Nordström, Jean-François Lemaître, Shin Okumura, Satoshi Chiba, and Arjan Koning. "Prompt-fission observable and fission yield calculations for actinides by TALYS." EPJ Web of Conferences 292 (2024): 08004. http://dx.doi.org/10.1051/epjconf/202429208004.

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The nuclear reaction code TALYS adopts the Hauser-Feshbach statistical decay theory, to de-excite fission fragments. This involves for instance the evaporation of prompt fission neutrons and γ-rays. TALYS incorporates databases of primary fission fragment distribution which consists of primary fission fragment yield and data for excitation energy distribution of fission fragments. We conducted a sensitivity study on three parameters in TALYS and fitted them in order to reproduce experimental and evaluated data, in thermal neutron-induced fission of 235U. Moreover, we demonstrate a large-scale calculation of average prompt neutron and γ-ray multiplicities for 243 selected actinide isotopes.

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Vorobyev, Alexander, Oleg Shcherbakov, Alexei Gagarski, Gennadi’ski Val, and Tatiana’mina Kuz. "Experimental estimation of the “scission” neutron yield in the thermal neutron induced fission of 233U and 235U." EPJ Web of Conferences 239 (2020): 05008. http://dx.doi.org/10.1051/epjconf/202023905008.

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The analysis of angular and energy distributions of prompt neutrons from the thermal neutron induced fission of 233U and 235U measured recently in the WWR-M research reactor (Gatchina, Russia) have been performed. The yield of “scission” neutrons has been estimated by comparing the measured distributions with calculations within the model of emission of neutrons from completely accelerated fragments. Besides taking into account “scission” neutrons, for the best description of measured angular and energy distributions of fission neutrons, the calculation should be performed under the assumption that neutrons with a higher (7-9%) probability are emitted along the fission axis in the center-of-mass system of fission fragments.

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Gatera, Angélique, Alf Göök, Franz-Josef Hambsch, André Moens, Andreas Oberstedt, Stephan Oberstedt, Goedele Sibbens, David Vanleeuw, and Marzio Vidali. "Prompt fissionγ-ray characteristics from neutron-induced fission on 239Pu and the time-dependence of prompt-γray emission." EPJ Web of Conferences 169 (2018): 00003. http://dx.doi.org/10.1051/epjconf/201816900003.

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Recent years have seen an increased interest in prompt fission γ-ray (PFG) measurements motivated by a high priority request of the OECD/NEA for high precision data, mainly for the nuclear fuel isotopes 235U and 239Pu. Our group has conducted a PFG measurement campaign using state-of-the-art lanthanum halide detectors for all the main actinides to a precision better than 3%. The experiments were performed in a coincidence setup between a fission trigger and γ-ray detectors. The time-of-flight technique was used to discriminate photons, traveling at the speed of light, and prompt fission neutrons. For a full rejection of all neutrons below 20 MeV, the PFG time window should not be wider than a few nanoseconds. This window includes most PFG, provided that no isomeric states were populated during the de-excitation process. When isomeric states are populated, PFGs can still be emitted up to 1 yus after the instant of fission or later. To study these γ-rays, the detector response to neutrons had to be determined and a correction had to be applied to the γ-ray spectra. The latest results for PFG characteristics from the reaction 239Pu(nth,f) will be presented, together with an analysis of PFGs emitted up to 200 ns after fission in the spontaneous fission of 252Cf as well as for thermal-neutron induced fission on 235U and 239Pu. The results are compared with calculations in the framework of the Hauser-Feshbach Monte Carlo code CGMF and FIFRELIN.

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10

Qi, L., J. N. Wilson, M. Lebois, A. Al-Adili, A. Chatillon, D. Choudhury, A. Gatera, et al. "Prompt fission gamma-ray emission spectral data for 239Pu(n,f) using fast directional neutrons from the LICORNE neutron source." EPJ Web of Conferences 169 (2018): 00018. http://dx.doi.org/10.1051/epjconf/201816900018.

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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.

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Seleznev, E., V. Bereznev, and I. Chernova. "PARTIAL NEUTRON TRANSPORT EQUATIONS." PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. SERIES: NUCLEAR AND REACTOR CONSTANTS 2019, no. 3 (September 26, 2019): 143–52. http://dx.doi.org/10.55176/2414-1038-2019-3-143-152.

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To analyze the spatial kinetics of the reactor, a system of equations for the spatial kinetics of the reactor, consisting of two equations, is usually used. One of them describes the behavior of the neutron flux density, and the second describes the behavior of the precursors of delayed neutrons. In this case, the density of the neutron flux includes the flux density prompt neutrons, appearing directly upon fission of the nucleus, and delayed neutrons that appear in the decay of some fission fragments. This system of equations is called classical. This paper considers the possibility of representing the neutron flux density in a nonstationary process by individual equations for prompt and delayed neutrons and presents the initial results of modeling the nonstationary process for dumping a control rod in a fast medium-power reactor. A system of equations describing such a behavior of the neutron field in a reactor is called a system of partial equations.

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12

Wilson, Jonathan, Damien Thisse, Matthieu Lebois, Nikola Jovancevic, Rhiann Canavan, Mathias Rudigier, David Étasse, and Rosa-Belle Gerst. "High resolution gamma-ray spectroscopy of fast-neutron induced fission." EPJ Web of Conferences 256 (2021): 00019. http://dx.doi.org/10.1051/epjconf/202125600019.

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Experiments to perform precision spectroscopy of fast neutron induced fission were carried out during the ν-Ball experimental campaign at the ALTO facility of IJC Laboratory Orsay. Low energy fission of 232Th(n,f), 238U(n,f) and spontaneous fission of 252Cf were studied using this hybrid highresolution spectrometer and calorimeter. New observables such as γ-ray multiplicity distributions correlated with specific fission fragments are presented and discussed. A new method using fast-timing techniques to detect prompt fission neutrons in coincidence with prompt fission γ-rays is described.

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Serot, Olivier, Olivier Litaize, and Abdelhazize Chebboubi. "Calculation of the fission observables in the resolved resonance energy region of the 235U(n,f) reaction." EPJ Web of Conferences 239 (2020): 05002. http://dx.doi.org/10.1051/epjconf/202023905002.

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Measurement of the fission fragments in coincidence with the emitted prompt neutrons was undertaken recently, at JRC-Geel institute, for the 235U(n,f) reaction in the resolved resonance energy region, up to 160 eV incident neutron energy. From this experimental work, fluctuations of several fission observables (mass yields, average total kinetic energy T̅K̅E̅, average prompt neutron multiplicity v̅P) were clearly observed. In the present work, these experimental pre-neutron fission fragment mass and kinetic energy distributions were used as input data for the FIFRELIN Monte Carlo code. By adopting the Hauser-Feshbach statistical model, the code simulates the de-excitation of the fission fragments. Four free parameters are available in the code: two of them (called RTmin and RTmax) govern at the scission point the sharing of the total available excitation energy between the two nascent fission fragments, while the two others (called σL and σH) assign the initial fission fragment spins. In this way, fission observables (prompt particles energy spectra and multiplicities, delayed neutrons multiplicity,. . . ) and correlations between them can be predicted and investigated. Here, these four free parameters were tuned in order to reproduce the average prompt neutron multiplicity at the resonance En=19.23 eV, resonance for which the experimental statistical uncertainty on v̅P is the lowest one. Then, the calculations were perfomed for all resonances by keeping the same set of free parameters. We show that the calculated fluctuations of v̅P in the resonances can rather be well reproduced by considering only the fluctuations of the pre-neutron mass yields and kinetic energy. In addition, from our calculation procedure, other fission observables fluctuations can also be predicted.

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Göök, Alf, Franz-Josef Hambsch, and Stephan Oberstedt. "Prompt fission neutron emission in the reaction 235U(n,f)." EPJ Web of Conferences 169 (2018): 00004. http://dx.doi.org/10.1051/epjconf/201816900004.

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Experimental activities at JRC-Geel on prompt fission neutron (PFN) emission in response to OECD/NEA nuclear data requests are presented in this contribution. Specifically, on-going investigations of PFN emission from the reaction 235U(n,f) in the region of the resolved resonances, taking place at the GELINA facility, are presented. The focus of this contribution lies on studies of PFN correlations with fission fragment properties. The experiment employs a scintillation detector array for neutron detection, while fission fragment properties are determined via the double kinetic energy technique using a position sensitive twin ionization chamber. This setup allows us to study several correlations between properties of neutron and fission fragments simultaneously. Results on PFN correlations with fission fragment properties from the present study differ significantly from earlier studies on this reaction, induced by thermal neutrons.

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15

Marini, P., J. Taieb, D. Neudecker, G. Bélier, A. Chatillon, D. Etasse, B. Laurent, et al. "Prompt fission neutron multiplicity in the ²³⁹Pu(n, f) reaction and its energy dependence." Journal of Physics: Conference Series 2586, no. 1 (September 1, 2023): 012035. http://dx.doi.org/10.1088/1742-6596/2586/1/012035.

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Abstract Measuring prompt fission neutrons to high precision is an experimental challenge, especially for radioactive fissioning nuclides. However, accurate average multiplicities, ν ¯ p , and kinetic energy distributions of prompt fission neutrons are essential for fundamental and applied nuclear physics. We present here a recent measurement of the 239Pu (n,f) ν ¯ p as a function of the incident-neutron energy, over the range 1-700 MeV. The measurement was performed with a cutting-edge setup and an innovative technique, which allowed to minimize and account for the main sources of bias. An unprecedented precision was therefore achieved. Our data are compared to GEF predictions as well as to evaluated libraries. For the first time, at low energies, the ENDF/B-VIII.0 nuclear data evaluation is validated with an independent measurement and the evaluated uncertainty reduced by up to 60%. This work paves the way to precisely measure prompt fission neutron multiplicities on highly radioactive nuclei.

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Kelly, Keegan J., Jaime A. Gomez, John M. O'Donnell, Matthew Devlin, Robert C. Haight, Terry N. Taddeucci, Shea M. Mosby, et al. "Observations of poorly-known features of the 239Pu and 235U prompt fission neutron spectra." EPJ Web of Conferences 239 (2020): 05010. http://dx.doi.org/10.1051/epjconf/202023905010.

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Prompt fission neutron spectrum (PFNS) evaluations use provide nuclear data for the PFNS across a wide range of incident and outgoing neutron energies. However, experimental data underlying the evaluation are sparse, inconsistent, and incomplete with respect to the desired incident and outgoing energy coverage. As such, evaluations sometimes predict features of the PFNS, such those relating to multi-chance fission and pre-equilibrium pre-fission neutron emission, without any experimental validation. The Chi-Nu experiment at Los Alamos National Laboratory has recently obtained high-precision results for the 239Pu and 235U PFNS which, for the first time in both cases, have shed light on multi-chance fission and pre-equilibrium contributions to the observed fission neutron spectrum. In addition to providing the first experimental data on some of these fission properties, the angular coverage of the Chi-Nu experiment allows for the extraction of angular distributions of pre-equilibrium pre-fission neutrons. PFNS results of multi-chance fission and pre-equilibrium pre-fission neutron emission are discussed in this proceedings in terms of the observed neutron spectrum and the average PFNS energies.

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Kulikov, G. G., A. N. Shmelev, and V. A. Apse. "Improving Nuclear Safety of Fast Reactors by Slowing Down Fission Chain Reaction." International Journal of Nuclear Energy 2014 (October 16, 2014): 1–18. http://dx.doi.org/10.1155/2014/373726.

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Light materials with small atomic mass (light or heavy water, graphite, and so on) are usually used as a neutron reflector and moderator. The present paper proposes using a new, heavy element as neutron moderator and reflector, namely, “radiogenic lead” with dominant content of isotope 208Pb. Radiogenic lead is a stable natural lead. This isotope is characterized by extremely low micro cross-section of radiative neutron capture (~0.23 mb) for thermal neutrons, which is smaller than graphite and deuterium cross-sections. The reflector-converter for a fast reactor core is the structure capable of transforming some part of prompt neutrons leaked from the core into the reflected neutrons with properties similar to those of delayed neutrons, that is, sufficiently large contribution to reactivity at the level of effective fraction of delayed neutrons and relatively long lifetime, comparable with lifetimes of radionuclides-emitters of delayed neutrons. It is evaluated that the use of radiogenic lead makes it possible to slow down the chain fission reaction on prompt neutrons in the fast reactor. This can improve the fast reactor safety and reduce some requirements to the technologies used to fabricate fuel for the fast reactor.

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Al-Adili, Ali, Kaj Jansson, Diego Tarrío, Franz-Josef Hambsch, Alf Göök, Stephan Oberstedt, Marc Olivier Frégeau, et al. "Studying fission neutrons with 2E-2v and 2E." EPJ Web of Conferences 169 (2018): 00002. http://dx.doi.org/10.1051/epjconf/201816900002.

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This work aims at measuring prompt-fission neutrons at different excitation energies of the nucleus. Two independent techniques, the 2E-2v and the 2E techniques, are used to map the characteristics of the mass-dependent prompt fission neutron multiplicity, v(A), when the excitation energy is increased. The VERDI 2E-2v spectrometer is being developed at JRC-GEEL. The Fission Fragment (FF) energies are measured using two arrays of 16 silicon (Si) detectors each. The FFs velocities are obtained by time-of-flight, measured between micro-channel plates (MCP) and Si detectors. With MCPs placed on both sides of the fission source, VERDI allows for independent timing measurements for both fragments. 252Cf(sf) was measured and the present results revealed particular features of the 2E-2v technique. Dedicated simulations were also performed using the GEF code to study important aspects of the 2E-2v technique. Our simulations show that prompt neutron emission has a non-negligible impact on the deduced fragment data and affects also the shape of v(A). Geometrical constraints lead to a total-kinetic energy-dependent detection efficiency. The 2E technique utilizes an ionization chamber together with two liquid scintillator detectors. Two measurements have been performed, one of 252Cf(sf) and another one of thermal-neutron induced fission in 235U(n,f). Results from 252Cf(sf) are reported here.

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19

Elter, Zs, and I. Pázsit. "Energy Correlation of Prompt Fission Neutrons." EPJ Web of Conferences 111 (2016): 05003. http://dx.doi.org/10.1051/epjconf/201611105003.

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Maslov, V. M. "Prompt-fission-neutrons spectra of 238U." Physics of Atomic Nuclei 71, no. 1 (January 2008): 9–26. http://dx.doi.org/10.1134/s106377880801002x.

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Svirikhin, A. I., A. V. Andreev, A. V. Yeremin, N. I. Zamyatin, I. N. Izosimov, A. V. Isaev, A. N. Kuznetsov, et al. "Prompt Neutrons from Spontaneous 254Rf Fission." Physics of Particles and Nuclei Letters 16, no. 6 (November 2019): 768–71. http://dx.doi.org/10.1134/s1547477119060311.

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Talou, P., T. Kawano, and I. Stetcu. "Prompt Fission Neutrons and γ Rays." Nuclear Data Sheets 118 (April 2014): 195–98. http://dx.doi.org/10.1016/j.nds.2014.04.035.

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Zeynalov, Shakir, Pavel Sedyshev, Valery Shvetsov, and Olga Sidorova. "Prompt Fission Neutron Investigation in 235U(nth,f) and 252Cf(sf) Reactions." EPJ Web of Conferences 211 (2019): 04003. http://dx.doi.org/10.1051/epjconf/201921104003.

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The prompt neutron emission in thermal neutron induced fission of 235U and spontaneous fission of 252Cf was investigated by using digital signal electronics. The goal was to check a new revised data analysis software with fission fragment (FF) kinetic energy corrections after prompt fission neutron (PFN) emission. The revised software was used to reanalyze old data measured in EC-JRC-IRMM, where 252Cf(sf) reaction was investigated. Both measurements were done using similar twin Frisch grid ionization chamber for fission fragment detection with equivalent NE213 fast neutron detector. About 0.5*106 FF with PFN coincidences have been analyzed in both measurements. The fission fragment kinetic energy, mass and angular distribution were investigated along with prompt neutron time of flight and pulse shape analysis using a six channel synchronous waveform digitizer (WFD) with sampling frequency of 250 MHz and 12 bit resolution in the 235U(nth,f) reaction. Similar WFD with sampling frequency of 100 MHz was used for PFN investigation in 252Cf(sf) reaction. These two experiments were considered as a reference for further investigations with a new setup composed of position sensitive ionization chamber to detect FF and an array of 32 liquid scintillators recently constructed in Dubna to detect neutrons.

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Marini, P., J. Taieb, D. Neudecker, G. Bélier, A. Chatillon, D. Etasse, B. Laurent, et al. "Multiplicity of prompt fission neutron in the ²³⁹Pu(n,f) reaction and its energy dependence." EPJ Web of Conferences 294 (2024): 02002. http://dx.doi.org/10.1051/epjconf/202429402002.

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Accurate multiplicities of prompt fission neutrons emitted in neutron-induced fission on a large energy range are essential for fundamental and applied nuclear physics. Measuring them to high precision for radioactive fissioning nuclides is, however, an experimental challenge. In this work, we extract the average prompt-neutron multiplicity emitted in the 239 Pu (n, f) reaction as a function of the incident-neutron energy, over the range 0.7-700 MeV. We used a novel technique, which allowed us to minimize and correct for the main sources of bias and thus achieve unprecedented precision. At low energies, our data validate, for the first time, the ENDF/B-VIII.0 nuclear data evaluation with an independent measurement and reduce the evaluated uncertainty by up to 60%. This work opens up the possibility of measuring, with high precision, prompt fission neutron multiplicities on highly radioactive nuclei relevant for energy production.

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Staples, P., J. J. Egan, G. H. R. Kegel, A. Mittler, and M. L. Woodring. "Prompt fission neutron energy spectra induced by fast neutrons." Nuclear Physics A 591, no. 1 (August 1995): 41–60. http://dx.doi.org/10.1016/0375-9474(95)00119-l.

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Kulikov, Gennady G., Anatoly N. Shmelev, Vladimir A. Apse, and Evgeny G. Kulikov. "On a significant slowing-down of the kinetics of fast transient processes in a fast reactor." Nuclear Energy and Technology 6, no. 4 (November 20, 2020): 295–98. http://dx.doi.org/10.3897/nucet.6.60379.

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The kinetics of nuclear reactors is determined by the average neutron lifetime. When the inserted reactivity is more than the effective delayed neutron fraction, the reactor kinetics becomes very rapid. It is possible to slow down the fast reactor kinetics by increasing the neutron lifetime. The authors consider the possibility of using the lead isotope, 208Pb, as a neutron reflector with specific properties in a lead-cooled fast reactor. To analyze the emerging effects in a reactor of this type, a point kinetics model was selected, which takes into account neutrons returning from the 208Pb reflector to the reactor core. Such specific properties of 208Pb as the high atomic weight and weak neutron absorption allow neutrons from the reactor core to penetrate deeply into the 208Pb reflector, slow down in it, and have a noticeable probability to return to the reactor core and affect the chain fission reaction. The neutrons coming back from the 208Pb reflector have a long ‘dead-time’, i.e., the sum of times when neutrons leave the reactor core, entering the 208Pb reflector, and then diffuse back into the reactor core. During the ‘dead-time’, these neutrons cannot affect the chain fission reaction. In terms of the delay time, the neutrons returning from the deep layers of the 208Pb reflector are close to the delayed neutrons. Moreover, the number of the neutrons coming back from the 208Pb reflector considerably exceeds the number of the delayed neutrons. As a result, the neutron lifetime formed by the prompt neutron lifetime and the ‘dead-time’ of the neutrons from the 208Pb reflector can be substantially increased. This will lead to a longer reactor acceleration period, which will mitigate the effects of prompt supercriticality. Thus, the use of 208Pb as a neutron reflector can significantly improve the fast reactor nuclear safety.

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Abdurrahman, Ibrahim, Matthew Kafker, Aurel Bulgac, and Ionel Stetcu. "Microscopic evidence for scission neutrons." EPJ Web of Conferences 292 (2024): 08008. http://dx.doi.org/10.1051/epjconf/202429208008.

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We discuss the neck rupture stage of fission and the emission of particles afterwards, two extremely rapid and highly non-equilibrium processes. Currently, the neck rupture cannot be directly probed by experiment, highlighting the importance of reliable theoretical predictions for this stage of fission. Time-dependent density functional theory (TDDFT) is used to simulate the spontaneous fission of 252Cf. In conjunction with statistical models, inputs from microscopic calculations can be used to make predictions for prompt neutron and gamma emission spectra, quantities which can be experimentally measured. Here we characterize the scission mechanism within TDDFT and estimate the number of scission neutrons and their kinetic energies.

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Oprea, C., M. A. Ahmad, J. H. Baker, and A. I. Oprea. "Mathematical Modeling of Neutron Induced Fission of 237Np Nucleus." Ukrainian Journal of Physics 67, no. 1 (February 10, 2022): 11. http://dx.doi.org/10.15407/ujpe67.1.11.

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Recent progress of applied and fundamental researches in nuclear physics necessitates new neutron sources with highly improved intensity. For a few years at JINR (Dubna) the development of new neutron facilities that will replace the IBR-2 neutron pulsed research reactor, which will finish its activities in 2032, is carried on. Some projects use the fission process induced by neutrons in neptunium-based fuels. In the present research, we will study the neutron-induced fission of 237Np nucleus. The cross-section, mass distribution, yields of isotopes of interest, average number of emitted prompt neutrons, neutron fission spectra, and other parameters are obtained. The mathematical modeling is done partially by using the theoretical models implemented in Talys software (TALYS-1.2) and by computer codes realized by the authors. The presented results are compared with the available data and are of interest in the JINR projects for the design of new neutron facilities destined for researches.

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29

Carjan, N., and M. Rizea. "Time-dependent decay rate and angular distribution of the scission neutrons by a dynamical approach." International Journal of Modern Physics E 28, no. 11 (November 2019): 1950103. http://dx.doi.org/10.1142/s0218301319501039.

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A dynamical model is employed to determine some peculiar properties of the scission neutrons, i.e., those emitted at the rupture of the neck between the fragments during low energy nuclear fission. Thus, by a specially adapted procedure, we calculate the time-dependent decay rate. This, defines the character of the emission process: pulsed or exponentially. From the time dependence of the survival probability, we deduced the “half-life” of the scission neutron emission. The angular distribution of the scission neutrons with respect to the fission axis is calculated as well. This is obtained for sets of neutron wave functions defined by a given quantum number [Formula: see text] (projection of the total angular momentum on the symmetry axis). A strong dependence on [Formula: see text] was found, namely, wave functions with different [Formula: see text] have different most probable emission angles: from emission along the fission axis (1/2) to emission perpendicular to the fission axis (9/2). This result leads to a new interpretation of the measured angular distribution of the prompt fission neutrons. Finally, an extension of the dynamical model (i.e., with a time-dependent potential also after scission) is presented.

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Talou, P., D. G. Madland, and T. Kawano. "Uncertainty Quantification on Prompt Fission Neutrons Spectra." Nuclear Data Sheets 109, no. 12 (December 2008): 2858–62. http://dx.doi.org/10.1016/j.nds.2008.11.023.

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31

Companis, I., L. Mathieu, M. Aïche, P. Schillebeeckx, J. Heyse, G. Barreau, S. Czajkowski, et al. "Use of Prompt Fission Neutrons for Measuring the Fission Efficiency." Physics Procedia 59 (2014): 167–72. http://dx.doi.org/10.1016/j.phpro.2014.10.026.

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32

Shmelev, A., V. Apse, G. Kulikov, and E. Kulikov. "ADVANTAGES OF THE FAST REACTOR CORE SURROUNDED BY THE PHYSICALLY THICK NEUTRON REFLECTOR MADE OF LEAD-208." PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. SERIES: NUCLEAR AND REACTOR CONSTANTS 2020, no. 4 (December 26, 2020): 46–59. http://dx.doi.org/10.55176/2414-1038-2020-4-46-59.

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The paper analyzes the effects produced by the use of lead isotope 208Pb instead of natural lead as a coolant and neutron reflector on neutron-physical parameters of fast reactor. A possibility is demonstrated to reach substantial (up to three orders of magnitude) elongation of mean prompt neutron lifetime in the fast reactor with physically thick 208Pb-reflector. So large elongation of prompt neutron lifetime opens an opportunity for remarkable enhancement of the reactor safety under conditions of reactivity-induced accidents. Numerical analyses have shown that it became possible to form high flux of slowed down and epithermal neutrons in 208Pb-reflector even at large distances from the reactor core. Spacious area of high neutron flux out of the reactor core may be used to transmute long-lived fission products and to produce significant quantities of necessary isotopes. Weak neutron absorption in 208Pb makes it possible to reach remarkable (up to 20 %) reduction of plutonium fraction in mixed uranium-plutonium fuel composition. It is proposed to place a layer with neutron absorber in 208Pb-reflector above the reactor core for the reactivity control with no variations in neutron-physical properties of the reactor core. If reactivity of the control rods in the reactor core is lower than effective fraction of delayed neutrons, then the reactor is obviously subcritical on prompt neutrons of the reactor core. In this case the danger of the reactivity-induced accident on prompt neutrons of the reactor core disappears. If the reactivity-induced accident is caused by joint action of the neutrons produced in the reactor core and in 208Pb-reflector, then the accident propagation will be substantially slowed down because of the longer lifetime of neutrons in 208Pb-reflector.

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33

Kopatch, Yuri, Vadim Novitsky, Gadir Ahmadov, Alexei Gagarsky, Daniyar Berikov, Gevorg Danilyan, Vladimir Hutanu, Jens Klenke, and Sergey Masalovich. "Measurement of the ROT effect in the neutron induced fission of 235U in the 0.3 eV resonance at a hot source of polarized neutrons." EPJ Web of Conferences 169 (2018): 00010. http://dx.doi.org/10.1051/epjconf/201816900010.

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The TRI and ROT asymmetries in fission of heavy nuclei have been extensively studied during more than a decade. The effects were first discovered in the ternary fission in a series of experiments performed at the ILL reactor (Grenoble) by a collaboration of Russian and European institutes, and were carefully measured for a number of fissioning nuclei. Later on, the ROT effect has been observed in the emission of prompt gamma rays and neutrons in fission of 235U and 233U, although its value was an order of magnitude smaller than in the α-particle emission from ternary fission. All experiments performed so far are done with cold polarized neutrons, what assumes a mixture of several spin states, the weights of these states being not well known. The present paper describes the first attempt to get “clean” data by performing the measurement of gamma and neutron asymmetries in an isolated resonance of 235U at the POLI instrument of the FRM2 reactor in Garching.

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34

Rubchenya, V. A. "A consistent model for describing prompt fission neutrons." Bulletin of the Russian Academy of Sciences: Physics 79, no. 7 (July 2015): 883–89. http://dx.doi.org/10.3103/s1062873815070199.

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35

Wilson, J. N., M. Lebois, P. Halipré, S. Oberstedt, and A. Oberstedt. "Prompt Emission in Fission Induced with Fast Neutrons." Physics Procedia 64 (2015): 107–13. http://dx.doi.org/10.1016/j.phpro.2015.04.014.

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36

Serot, Olivier, Olivier Litaize, and Abdelaziz Chebboubi. "Influence of scission neutrons on the prompt fission neutron spectrum calculations." EPJ Web of Conferences 146 (2017): 04027. http://dx.doi.org/10.1051/epjconf/201714604027.

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37

Mumpower, M. R., M. Verriere, A. E. Lovell, T. Kawano, I. Stetcu, and P. Talou. "The Los Alamos fission yield evaluation pipeline." EPJ Web of Conferences 242 (2020): 05002. http://dx.doi.org/10.1051/epjconf/202024205002.

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The nuclear data team at Los Alamos National Laboratory has undertaken a campaign to construct new fission yield evaluation. Significant advances have been made on a number of fronts. Nuclear potential energy surfaces can now be generated with the newly developed MicMac code based off the Finite Range Liquid-Drop Model (FRLDM). This model can be incorporated into the Los Alamos de-excitation framework codes BeOH and CGMF to perform modeling of prompt, independent (IFY) and cumulative (CFY) fission yields that take into account prompt and beta-delayed neutrons and photons consistent with decay data. This is in stark contrast to what exists in evaluated nuclear data libraries today, where only a few incident energy points are used with limited physical insights and no consistency between IFY, CFY and decay data. We highlight the latest progress with application of neutron-induced fission of 235 U and 239 Pu.

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38

Yuferov, Anatoly G. "On the concept of “effective delayed neutron fraction”." Nuclear Energy and Technology 8, no. 4 (December 13, 2022): 275–79. http://dx.doi.org/10.3897/nucet.8.96567.

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The article considers methodological issues related to the conceptual and terminological apparatus of the dynamics of nuclear reactors. Based on an elementary analysis of the standard point reactor kinetics equations, the author shows that it is necessary to clarify the physical meaning of the parameter β included in the equations, which is traditionally interpreted as the “effective delayed neutrons fraction” (EDNF). It follows directly from the kinetics equations that the parameter β, which appears in these equations as the EDNF, is, from the point of view of the neutron balance, the fraction of prompt neutrons consumed for the generation of delayed neutron precursors (DNPs), and, from the point of view of the DNP balance, the DNP yield per prompt neutron in a single fission event. With these interpretations taken into account, the role of the β parameter is considered in situations related with its adjustment by multiplying it by the “delayed neutron efficiency factor” and with the establishment of the actual fractions of prompt and delayed neutrons. In particular, it is shown that: the statement “if the delayed neutron fraction is β, then the prompt neutron fraction is equal to 1 – β”, used in the problems of analyzing the nuclear reactor dynamics as a starting position, cannot be considered applicable to any reactor conditions; an increase in the β parameter by multiplying it by the “delayed neutron efficiency factor” leads, contrary to traditional interpretations, not to an increase but to a decrease in neutron reproduction in a supercritical reactor. The proposed clarifications are appropriate both in terms of more adequate descriptions of processes in nuclear reactors and in relation to the formulations of nuclear safety requirements.

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39

MÄrten, H., and A. Ruben. "Prompt fission-neutron spectra in the reactions of 1.5-MeV neutrons with235U." Soviet Atomic Energy 69, no. 1 (July 1990): 583–87. http://dx.doi.org/10.1007/bf02086945.

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40

Carjan, N., and M. Rizea. "Why not: Prompt Fission Neutrons are Released at Scission." Physics Procedia 64 (2015): 40–47. http://dx.doi.org/10.1016/j.phpro.2015.04.006.

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41

Talou, P., and T. Kawano. "Advanced Modeling of Prompt Fission Neutrons and Gamma Rays." EPJ Web of Conferences 2 (2010): 08005. http://dx.doi.org/10.1051/epjconf/20100208005.

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42

Maslov, V. M., N. A. Tetereva, V. G. Pronyaev, A. B. Kagalenko, K. I. Zolotarev, R. Capote, T. Granier, B. Morillon, F. J. Hambsch, and J. C. Sublet. "Spectrum of prompt fission neutrons from 235U(n, F)." Atomic Energy 108, no. 6 (October 30, 2010): 432–43. http://dx.doi.org/10.1007/s10512-010-9313-0.

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43

Pradana, Luqman Satria, Utari Utari, Suharyana Suharyana, and Azizul Khakim. "ESTIMATION OF NEUTRON AND PROMPT PHOTON DOSE RATE DISTRIBUTION IN TMSR-500 USING MCNP6." JURNAL TEKNOLOGI REAKTOR NUKLIR TRI DASA MEGA 24, no. 3 (November 9, 2022): 107. http://dx.doi.org/10.17146/tdm.2022.24.3.6692.

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Thorium Molten Salt Reactor-500 (TMSR-500), one of the Generation IV nuclear reactors, is designed by Thorcon International, Pte. Ltd, which is projected to be built in Indonesia. The reactor core is radially surrounded by B4C shielding, but not the upper part. As the silo hall sits above the reactor core and is accessible by reactor personnel, the dose rate must be calculated in the area to ensure the workers receive an annual dose below the acceptable limit. The dose rate from neutrons and photons as the result of fission reactions are the only sources to be calculated in this research, without taking the source from fission products into account. This research aims to obtain the dose rate distribution of neutrons and prompt photons using Monte Carlo code MCNP6. The reactor was assumed to operate at a nominal thermal power of 557 MWth. Dose rate calculation was obtained from flux Tally F4 and converted into dose rate using Dose Energy Dose Function (DEDF) factor. Conversion factors of flux to the dose were based on ICRP-21 and ANSI/ANS-6.1.1 1977. The result of the calculations showed that the distribution of neutron and prompt photon fluxes does not reach the silo hall.

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44

Kulikov, Gennady G., Anatoly N. Shmelev, Vladimir A. Apse, and Evgeny G. Kulikov. "Safety features of fast reactor with heavy atomic weight weakly neutron absorbing reflector." Nuclear Energy and Technology 6, no. 1 (March 11, 2020): 15–21. http://dx.doi.org/10.3897/nucet.6.50867.

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The purpose of the present study is the justification of the possibility of improving fast reactor safety by surrounding reactor cores with reflectors made of material with special neutron physics properties. Such properties of 208Pb lead isotope as heavy atomic weight, small neutron absorption cross section, and high inelastic scattering threshold result in certain peculiarities in neutron kinetics of the fast reactor equipped with 208Pb reflector, which can significantly enhance reactor safety. The reflector will also make possible generation of additional delayed neutrons characterized by the “dead” time. This will improve the resistibility of the fission chain reaction to stepwise reactivity excursions and exclude prompt supercriticality. Let us note that generation of additional delayed neutrons can be shaped by reactor designers. The relevance of the study amounts to the fact that generation of additional delayed neutrons in the reflector will make it possible mitigating the consequences of a reactivity accident even if the introduced reactivity exceeds the effective fraction of delayed neutrons. At the same time, the role of the fraction of delayed neutrons as the maximum permissible reactivity for reactor safety is depreciated. Scientific originality of the study pertains to the fact that the problem of yield of additional neutrons with properties close to normal delayed neutrons, has not been posed before. The authors suggest a new method for enhancing safety of fast reactors by increasing the fraction of delayed neutrons due to the time delay of prompt neutrons during their transfer in the reflector. In order to benefit from the expected advantages, the following combination is acceptable: lead enriched by 208Pb is used as a neutron reflector while natural lead or other material (sodium, etc.) is used as a coolant in the reactor core.

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45

Oprea, Cristiana, Mohammad Ayaz Ahmad, Alexandru Ioan Oprea, Jalal H. Baker, and Naima Amrani. "Nuclear Reaction Mechanisms of Neutron Induced Fission of 237Np Nucleus." European Journal of Engineering Science and Technology 4, no. 4 (December 20, 2021): 15–24. http://dx.doi.org/10.33422/ejest.v4i4.600.

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At FLNP JINR Dubna new prospects for developing new neutron facilities have already been started, that will replace the IBR-2 neutron pulsed research reactor which shut down in the year 2032. Several agreed projects use the fission processes induced by neutrons on neptunium-based fuels. An investigation of the neutron fission process on the 237Np nucleus was conducted in the present research. Several parameters were analyzed during neutron-induced fission of 237Np including the neutron cross-section, mass distributions, prompt neutron emission, isotope production, and neutron spectra. Evaluations of the above observables were conducted using TALYS – 9.1 Software, with incident neutron energies ranging from 0.4 to 25 MeV. The exact value of cross-section was obtained as 5 – 5.5 MeV in the present work, whereas from literature, it was found up to 10 MeV. Neutron spectra were analyzed and separated contributions from different nuclear reaction mechanisms were obtained. Our investigations have revealed some important yields and isotope production cross-sections that were in good agreement with literature data.

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46

Nishio, K., H. Yamamoto, I. Kanno, I. Kimura, and Y. Nakagome. "A system for correlation measurement of fission fragments and prompt neutrons for thermal neutron induced fission." Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 385, no. 1 (January 1997): 171–78. http://dx.doi.org/10.1016/s0168-9002(96)00932-1.

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47

Okumura, Shin, Toshihiko Kawano, and Satoshi Chiba. "The fission yield calculations with Langevin model, Hauser-Feshbach statistical decay, and beta decay." EPJ Web of Conferences 239 (2020): 03005. http://dx.doi.org/10.1051/epjconf/202023903005.

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We performed the calculations of de-excitation of the primary fission fragments by the Hauser-Feshbach statistical decay followed by the β decay of de-excited fission products. We used the primary fission fragment mass distributions YP(A), total kinetic energy TKE(A), and its width σTKE(A) as input, which were calculated with the Langevin model using macroscopic-microscopic models of the potential energy surface. The prompt neutron multiplicity v̅ and the independent fission product yield (FPY) YI(Z, A, M) and cumulative FPY YC(Z, A, M) are calculated by the Hauser-Feshbach statistical decay and β decay calculations, respectively. The calculated v̅ was overestimated approximately 17% compared to the evaluated data. The decay heats from β and γ were in accordance with the experimental results. The β delayed neutrons yieild was also overestimated.

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48

Al-Adili, A., D. Tarrío, F. J. Hambsch, A. Göök, K. Jansson, A. Solders, V. Rakopoulos, et al. "Analysis of prompt fission neutrons in235U(nth,f) and fission fragment distributions for the thermal neutron induced fission of234U." EPJ Web of Conferences 122 (2016): 01007. http://dx.doi.org/10.1051/epjconf/201612201007.

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49

Nix, J. Rayford, David G. Madland, and Arnold J. Sierk. "Effect of fission dynamics on the spectra and multiplicities of prompt fission neutrons." Radiation Effects 92, no. 1-4 (March 1986): 263–76. http://dx.doi.org/10.1080/00337578608208336.

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Neudecker, D., P. Talou, T. Kawano, A. C. Kahler, M. E. Rising, and M. C. White. "Evaluating the239Pu Prompt Fission Neutron Spectrum Induced by Thermal to 30 MeV Neutrons." EPJ Web of Conferences 111 (2016): 05004. http://dx.doi.org/10.1051/epjconf/201611105004.

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Journal articles on the topic 'Prompt Fission Neutrons'

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