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We apply the Cassini shape parameterization to the dynamical study of actinide fission using the multi-dimensional Langevin equation. The fragment mass distributions for fission of 236U and 256, 258 Fm are calculated with the 4D Langevin equation. The 4D collective space is formed by adding either α3 or α6 to the basic 3D {α, α1, α4} space. We investigate the role of α3 and α6 by comparing the results of 4D (α3 or α6) with that of 3D. For 236U and 256Fm, where asymmetric fission is predominant, the fragment mass distributions calculated in the 4D (α3) space are in good agreement with experimental data. On the other hand, for 258Fm, which is characterized by symmetric fission, 4D (α6) is effective for describing the shape of compact symmetric fragments. We demonstrate the advantages of the Cassini shape parameterization for the dynamical study of actinide fission. [ABSTRACT FROM AUTHOR]

An evaluation of the average prompt fission neutron multiplicity, ν¯ p, of 239Pu(n,f) is shown. This evaluation includes (a) the correlated fission model CGMF, and (b) a detailed analysis of past and recently published experimental data. Using CGMF-calculated ν¯ pas prior enables to link, through the use of evaluated model input parameters, ν¯ p to other fission observables such as the prompt fission neutron spectrum (PFNS), pre-neutron emission fission yields as a function of mass, and the average total kinetic energy of the fragments. These evaluated parameters produce realistic predictions of many fission observables, while the evaluated ν¯ p agrees well (χ2 ≈ 1) with data. Moreover, with the new evaluated ν¯ p, the effective neutron multiplication factor of fast Pu ICSBEP critical assemblies are predicted with a mean bias of 58 pcm compared to 18 pcm with ENDF/B-VIII.0, when paired with a new 239Pu PFNS and fission cross section. Due to these encouraging validation results, the evaluated ν¯ p is currently part of a release candidate for the 239Pu ENDF/B-VIII.1 file. Hence, a correlated fission model was used for the first time for evaluating ν¯ p that is of evaluation quality. This is an important step towards consistent evaluations of prompt fission observables. [ABSTRACT FROM AUTHOR]

A new measurement of the 235U(n,f) fission cross section was carried out at n_TOF. The experiment covered the neutron energy range from 10 MeV up to 500 MeV, and it used the 1H(n,n) cross section as normalization for the neutron fluence measurement. In this contribution, the measurements and the characterization of the detectors covering the incident energy range up to 150 MeV are discussed. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The systematic evaluations of spectrum averaged cross sections of dosimetric reactions over a broad range of energies were performed in 252Cf (spontaneous fission) and 235U(nth,f) neutron fields. The neutron sources used in this study were LR-0, VR-1 zero power research light water reactors, LVR-15 10 MW research light water reactor, and 252Cf neutron source with emission specified precisely by the manganese sulphate bath. All spectral averaged cross sections were inferred from measured reaction rates which were derived from gamma spectrometry. These gamma spectrometry measurements were performed using a single detector in all cases. The ratios of 252Cf and 235U spectral averaged cross sections can be used to specify the high energy tail of the 235U prompt fission neutron spectrum as the 252Cf spontaneous fission spectrum is considered as a standard. Furthermore, ratios are independent of cross section uncertainties since uncertainties in the cross sections are eliminated. Theoretical models of fission can be tested based on our measurements. The calculations were performed in MCNP6.2 transport code using different prompt fission neutron spectra and IRDFF-II cross sections for threshold reactions. The ratios are in good agreement using only ENDF/B-VIII.0 235U prompt fission neutron spectrum suggesting it to be harder than in other evaluations. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In the last decades, measurements of spallation, fragmentation and Coulex induced fission reactions in inverse kinematics have provided valuable data to accurately investigate the fission dynamics and nuclear structure at large deformations of a large variety of stable and non-stable heavy nuclei. To go a step further, we propose now to induce fission by the use of quasi-free (p,2p) scattering reactions in inverse kinematics, which allows us to reconstruct the excitation energy of the compound fissioning system by using the four-momenta of the two outgoing protons. Therefore, this new approach might permit to correlate the excitation energy with the charge and mass distributions of the fission fragments and with the fission probabilities, given for the first time direct access to the simultaneous measurement of the fission yield dependence on temperature and fission barrier heights of exotic heavy nuclei, respectively. The first experiment based on this methodology was realized recently at the GSI/FAIR facility and a detailed description of the experimental setup is given here. [ABSTRACT FROM AUTHOR]

A specific objective of the recent IAEA Coordinated Research Project on Photonuclear Data and Photon Strength Functions (Code F41032; Duration 2016-2019) has been to measure photonuclear cross-section data where needed, for unexplored nuclei and cases of discrepant existing data. A dedicated experimental campaign has been conducted at the laser Compton-scattering γ-ray source of the NewSUBARU synchrotron radiation facility of SPring8, Japan, where photoneutron reactions for 11 nuclei from 9Be to 209Bi have been investigated in the Giant Dipole Resonance energy region. The measurements followed the development of a flat-effi ciency moderated neutron detection array and the associated neutron-multiplicity sorting techniques. The IAEA CRP campaign has been followed at NewSUBARU by new measurements of photofission and photoneutron reactions on 238U and 232Th in the energy range of 5.87 MeV – 20.14 MeV. The neutron-multiplicity sorting of high-multiplicity fission neutron coincidence events has been performed using a dedicated energy dependent, multiple firing statistical treatment. The photoneutron (γ, xn) and photofission (γ, fxn) reactions have been discriminated by considering a Gaussian distribution of prompt-fission-neutrons (PFN) multiplicities predicted by the evaporation theory. We here provide preliminary experimental (γ, n), (γ, 2n) and (γ, F) cross sections, average energies of PFN and of photoneutrons emitted in (γ, n) and (γ, 2n) reactions, as well as the mean number of PFN per fission act. The new 238U cross sections are compared with recent statistical-model calculations performed with the EMPIRE code on existing data. [ABSTRACT FROM AUTHOR]

During the last decade, the use of inverse kinematics in the experimental study of fission is bringing a wealth of new observables obtained in single measurements, allowing their analysis and their correlations. An ongoing application of this technique is the basis of a series of experiments performed with the variable-mode, large-acceptance VAMOS++ spectrometer at GANIL. A recent experiment has been focused on the survival of the nuclear structure effects at high excitation energy in fission and quasi-fission. The full isotopic identification of fragments, the fission dynamics and the ratio between the production of fragments with even and odd atomic numbers, the so-called proton even-odd effect, are shown. The latter shows a different mechanism for fission and quasi-fission that could be used to separate fission from quasi-fission. [ABSTRACT FROM AUTHOR]

Measurements of independent fission yield distributions in neutron-induced fission at high neutron energies are important for our fundamental understanding of the fission process, and are also relevant for reactor physics applications. So far, measurements of independent fission yields in proton-induced fission have been performed at the IGISOL facility at the University of Jyväskylä, using the Penning trap as a high resolving-power mass-filter. In order to also facilitate measurements of neutron-induced fission, a dedicated ion guide and a proton-to-neutron converter was developed. However, the first measurement indicates that fewer fission products than expected reach the Penning trap. To explore potential reasons and possible improvements, a simulation model was also developed and benchmarked. The benchmark showed that the model is able to reproduce the performance of the ion guide remarkably well and that the main reason for the low yield of fission products is the low collection efficiency of the ion guide. Based on the benchmark, a new ion guide is being designed. In the new design, the positions of the uranium targets and volume of the ion guide have been changed to increase the collection of fission products. This results in a five-fold increase of the yield. However, the collection efficiency of the new ion guide still needs to be improved in order to achieve intensities of the extracted fission products that are large enough to allow for reasonable measurement times. Because the volume of the ion guide is increased significantly, the extraction time of the ions is expected to be longer than that from the previous ion guide. Therefore, an electric field guidance system that consists of a combination of a stationary electric field and an RF-carpet is considered to be deployed. The stationary field, produced from a set of DC-ring electrodes, accelerates the ions towards the RF-carpet at end plate of the ion guide. The RF-carpet consists of a time-dependent field, produced from a radio-frequent structure of concentric rings, with a DC-component that guides the ions towards the exit hole in the center of the end plate. In this paper we present the current status of the simulations and design of the new ion guide. [ABSTRACT FROM AUTHOR]

We have extended significantly the microscopic description of the fission process by examining a larger set of observables. We extract neutron and proton numbers of fission fragments, their spins and fission fragment relative orbital angular momentum and their correlations, investigate neutrons emitted at or shortly after scission, excitation energy sharing mechanism, total kinetic energy of fission fragments, and the entanglement entropy. I will present a short overview of our simulations obtained with two independent nuclear energy density functionals. [ABSTRACT FROM AUTHOR]

Nuclear fission is expected to play an essential role in the r-process nucleosynthesis via the fission recycling process. However, the impact of the fission recycling process on the r-process is still unclear due to the ambiguity of the fission yields for nuclei far from the beta-stability line and superheavy nuclei. Our four-dimensional Langevin model can reproduce experimental nuclear fission properties, such as fission fragment mass distributions and total kinetic energies in a systematic manner including their sudden changes due to shell structure. Then we developed a phenomenological yield model for nuclei Z=92 to 122, ranging from neutron deficient to very neutron-rich ones, by fitting the fission fragment mass yield obtained by the Langevin model with five Gaussians. We use the charge distributions for each isobar based on a parametrization which we have evaluated based on thousands of experimental data for actinides, to obtain the fission yields in the form of (Z, N) distributions. What is unique here is the sudden change of the mass distribution from a 2-peak to 1-peak structure for the region of 256Fm, and the appearance of a 5-peak structure for superheavy nuclei predicted by the 4D Langevin calculation. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We investigated theoretical methods to estimate the charge polarization of the fission fragments. The method is based on the microscopic mean-field model with the nucleon degree of freedom, and is represented in the three-dimensional coordinate space for dealing with any nuclear deformation. We employed the Skyrme effective interaction for the calculations and uranium-236 as a target nucleus. We reported static and dynamic methods in which the potential energy surface of the fissioning nucleus concerning the quadrupole and octupole deformations are used. Although the static method deduced the charge polarization which indicates the nuclei with the magic number and the octupole deformation, the quantities are not consistent with the existing data library (Wahl's systematics). The dynamic method with the iso-energy initial condition on the potential energy surface showed the finite charge polarization of light and heavy fission fragments which is consistent with the data library. Furthermore, it indicates that the charge polarization has energy dependence of the initial states of the dynamic method. [ABSTRACT FROM AUTHOR]

We present first preliminary results of a novel method for measuring independent isotopic fission yields (IIFYs) of spontaneous fission (SF) via direct mass measurements, at the FRS Ion Catcher (FRS-IC) at GSI. Fission products were generated from a 252Cf source installed in a cryogenic stopping cell, and were identified and counted with the multiple-reflection time-of-flight mass spectrometer (MR-TOF-MS) of the FRS-IC, utilizing well-established measurement and data analysis methods. The MR-TOF-MS resolves isobars unambiguously, even with limited statistics, and its non-scanning nature ensures minimal relative systematic uncertainties amongst fission products. The analysis for extracting IIFYs includes isotope-dependent efficiency corrections for all components of the FRS-IC. In particular, we applied a self-consistent technique that takes into account the element-dependent survival efficiencies in the CSC, due to chemical reactions with the buffer gas. Our IIFY results, which cover several tens of fission products in the less-accessible high-mass peak (Z = 56 to 63) down to fission yields at the level of 10−5, are generally similar to those of the nuclear database ENDF/B-VII.0. Nevertheless, they reveal some structures that are not observed in the database smooth trends. These are the first results of a planned campaign to investigate IIFY distributions of spontaneous fission at the FRS-IC. Upcoming experiments will extend our results to wider Z and N ranges, lower fission yields, and other spontaneously-fissioning actinides. [ABSTRACT FROM AUTHOR]

We present our first results for a microscopic simulation of symmetric boost fission in terms of the antisymmetrized molecular dynamics (AMD) model. In AMD model, ground states of fissioning nuclei were prepared by a frictional cooling method and symmetrical boost momenta were given to nucleons inside to split the ground-state into fission fragments. After the simulation, we calculated the mass numbers and total kinetic energy (TKE) of the fission fragments. We also calculated orbital angular momenta of each fragment and identified them as spins, their mutual orientation and their orientation with respect to the linear momenta which defined the fission axis. Moreover, we found spin distribution of fission fragments was similar to the one given by the Fermi-gas model if spin cut-off parameter was adjusted. Finally, several ternary fission events were observed, emitting Tritium or 4He from the neck region, and average energy and angles of these ternary particles with respect to the fission axis were found to be in accord with experimental data. [ABSTRACT FROM AUTHOR]

As a fissioning nucleus approaches scission, the angular-momentum bearing modes in the evolving dinuclear complex may be agitated by multiple transfers of individual nucleons. It is discussed how this mechanism populates the various rotational modes at different rates and leads to fragment angular momenta that are preferentially perpendicular to the fission axis but mutually largely uncorrelated. Using the fission simulation code FREYA, it is demonstrated how a measurement of the angular distribution of photons from identified collective transitions in the product nuclei can provide quantitative information on the relative importance of the twisting mode in fission. [ABSTRACT FROM AUTHOR]

The study of nuclear fission yields has a major impact on the characterization and understanding of the fission process and is mandatory for reactor applications. In the framework of a collaboration between the CEA, the LPSC and the ILL, a program of actinide fission yield measurements has been ongoing for several years at the LOHENGRIN spectrometer. However, the measurement of very low fission yields in the symmetry region and the heavy wing of the distributions is difficult to achieve due to the strong contamination by other masses with much higher yields and requires the development of a new experimental setup. This paper will first present the results of a new absolute measurement of the 235U(nth,f) mass yields using an ionization chamber placed at the exit of the spectrometer. Although very well documented in the literature, these yields show uncertainties lying from 3% to 10% with large discrepancies between libraries and a lack of correlation matrices. New experimental data obtained at the LOHENGRIN spectrometer will be detailed, along with the measurement method and the production of the experimental covariance matrix. The second part will show the development of a Time of Flight (ToF) line in order to improve the background rejection in the mass yield measurements. In the symmetry region, the precision of the measurement is limited by the background estimation due to the charge exchanges with the residual gas of the separator. We plan to analyze the events using a triple coincidence (∆E x E) x ToF, whereas today only (∆E x E) selection is available. The new ToF line is built using Si3N4 foils and secondary electron detectors (SED) for the start and stop detectors. We will present the choices made for the SED technology along with the progress achieved on the ToF line characterization. [ABSTRACT FROM AUTHOR]

Low energy fission of 234,235,236,238U and 237,238Np radioactive beams, provided by the GSI/FRS facility, has been studied using the R3B/SOFIA setup. The latter allows, on an event-by-event basis, to simultaneously identify, in terms of their mass and atomic numbers, the fissioning nucleus in coincidence with both fission fragments after prompt-neutron emission. This presentation reports on new results on elemental, isobaric and isotopic yields. [ABSTRACT FROM AUTHOR]

Reaction measurements on fission products are being planned at both Argonne National Lab and at the Facility for Rare Isotope Beams. These indirect experiments produce specific short-lived nuclei via beta decay, and the subsequent neutron and gamma emission are studied. Some initial experiments found a surprising overabundance of gamma emission, which theory has yet to explain. To remedy this, we are developing an integrated nuclear data workflow that connects advanced nuclear shell model codes for describing the beta decay with a contemporary nuclear reaction model code. [ABSTRACT FROM AUTHOR]

The study of the 242Pu fission cross section has become more important since this isotope is present in Pressurized Water Reactor Uranium Oxide and Mixed Oxide fuel, as well as in fast neutron reactors fuel. This nucleus has been also selected for monitoring the high neutron flux RJH reactor (CEA-Cadarache). For all these reasons, the fission cross section structure of this fertile isotope, and especially its class-II states resonances were investigated in this work. Two class-II states have been identified in the Resolved Resonance Range (RRR) and their parameters have been supplied to the CONRAD code. 68 class- II states have been identified in the Unresolved Resonant Range (URR) and their parameters have been added in the TALYS code data library to reproduce as well as possible the experimental fission cross section. The methodology to identify and insert the class-II states in RRR and URR is described here. [ABSTRACT FROM AUTHOR]

The CONRAD computer code is being developed by the nuclear data group of CEA Cadarache since mid-2000. It was originally designed to analyse neutron-induced reactions in the resonance energy range and then, was extended to higher energies (several MeV) treatment with inclusion of charged-particles penetration factor. In the thermal energy range, a procedure was implemented to manage the so-called Thermal Neutron Constants, especially devoted to the 239Pu, 241Pu, 233U and 235U nuclei. In the resonance range, nuclear models implemented in the CONRAD program rely on R-matrix model fits with in particular, improved treatment of the fission penetration factor and fluctuations of the prompt neutron multiplicity via a two-step (n,γf) process. Above the resonance range, the neutron continuum energy region of the observed cross sections can be analysed either with the TALYS code or with an in-house optical model code named CCCP that is followed by Hauser-Feshbach calculations according to the compound nucleus deexcitation channels. Non-model least squares fitting procedures have been also tested for neutron cross sections adjustment in the continuum energy range, and such, applied in the framework of the standard cross section group at the IAEA (Vienna). This paper will only focus on the evaluation works performed in the resonance range of minor and major actinides with special emphasis on the experimental corrections suitable to reproduce time-of-flight experiments. [ABSTRACT FROM AUTHOR]

The accurate determination of reactor antineutrino spectra remains a very hot research topic, where new questions have emerged in recent years. Indeed, after the "reactor anomaly" – a deficit of measured antineutrinos at short baseline reactor experiments with respect to spectral predictions – the three international reactor neutrino experiments Double Chooz, Daya Bay and Reno have evidenced spectral distortions in their measurements with respect to the same spectral predictions. This puzzle is called the "shape anomaly". Recently summation calculations of reactor antineutrino spectra based on the use of nuclear data have obtained the best agreement to date with the reactor neutrino flux measurements at the level of 2% thanks to a decade of Total Absorption Gamma-ray Spectroscopy (TAGS) measurements at the radioactive beam facility of the University of Jyväskylä in two experimental campaigns. A selection of the results obtained so far is presented. [ABSTRACT FROM AUTHOR]

Uranium-233 plays an important role in the Th-U fuel cycle, which has been proposed as an alternative to the U-Pu fuel cycle due to its reduced amount of transuranium elements. The available experimental 233U(n,γ) cross section data in the literature are scarce, [1–3]. In 2008, the 233U(n,γ) cross section was investigated at LANL using the DANCE detector combined with a PPAC, however the statistics in the keV regime were inadequate for a reliable extraction of the cross section at 100 keV. An accurate measurement of the 233U(n,γ) cross section is required by the NCSP to complete the neutron-induced cross section data; a new evaluation reported the need of 233U capture data. The challenge in this measurement lies in the difficulty of measuring capture cross section data due to the competing capture and fission channels. Fission reactions are around one order of magnitude more likely than capture for 233U. The accuracy in the capture cross section measurement relies on the discrimination between the γ-rays produced in capture and fission reactions, for which an experimental setup combining capture and fission detectors is needed. Following this requirement, a new measurement has been performed at LANSCE combining the γ-ray array DANCE with the neutron detector NEUANCE to identify fission and neutron-capture events. This measurement will provide results of the 233U capture-to-fission ratio in the Resolved and Unresolved Resonance regions. [ABSTRACT FROM AUTHOR]

The zero-power reactor MINERVE (CEA Cadarache) was designed to perform reactivity worth measurements by the oscillation technique. The various experimental programs, undertaken for the last thirty years, involved cylindrical samples with a diameter of about 1 cm and a height ranging from a few cm to 10 cm. Most of the samples are composed of UO2 pellets mixed with a high neutron absorbing nuclide, i.e. fission product, actinide, in a double-sealed Zry-4 container. An experimental program started in 2015 in collaboration with the Joint Research Centre of Geel to study the MINERVE samples at the time-of-flight facility GELINA by the neutron transmission technique. The two main objectives consist of checking both the composition of the MINERVE samples provided by the manufacturer and the quality of the resonance parameters recommended in the evaluated neutron data library JEFF-3.3. The pioneer experiments on MINERVE samples containing 107Ag and 109Ag revealed a substantial Tungsten contamination that was not reported by the manufacturer. Such a Tungsten contamination is related to the manufacturing process of the sample pellets. The observed Tungsten contaminations lead to non-negligible increases of the C/E ratios up to a few percent. second experimental campaign on MINERVE samples containing 99Tc provided useful insight on the quality of the 99Tc resonance parameters measured at the GELINA facility at the end of the 90s. The ongoing program continuing through 2022 will deliver data for samarium (natural, 147, 149, 152), neodymium (natural,143,145), gadolinium (natural, 155), europium (151, 153), rhodium (103), cesium (133), hafnium (180), dysprosium (160, 161, 162, 163, 164) and erbium (168, 170). The present work focuses on the data analysis technique developed for long cylindrical samples with a diameter smaller than the neutron beam, and on the grain size distribution model implemented in the resonance shape analysis REFIT. [ABSTRACT FROM AUTHOR]

A novel method was developed to separate the 238U fission contribution measured in quasi-differential time-of-flight scattering experiments in order to isolate the elastic and inelastic events. Pulse height distributions from in-beam measurements were used to generate response functions, which were used to reconstruct the 238U prompt fission neutron spectra. This method was validated by reconstructing the measured 252Cf spontaneous fission pulse height distribution. Monte Carlo calculations were used to model the experiment. Good agreement was observed between the measured and calculated 238U fission contribution. [ABSTRACT FROM AUTHOR]

Accurate actinides fission cross sections around 1 MeV are of primary importance for the safety of generation IV reactors. To have accurate measurements, the neutron flux must also be accurately estimated. This is usually done with respect to the 235U(n,f) cross section. It is however possible to measure the neutron flux with respect to the 1H(n,n)p cross section which is a primary standard, providing an independent and precise measurement. Typically, the usual proton recoil technique uses a silicon detector for neutrons of energy between 1 and 70 MeV. However, the high electron and gamma background due to neutron production under irradiation makes the use of this or any other detector not suitable for an accurate measurement below 1 MeV. To this end, the Gaseous Proton Recoil Telescope is developed and characterized. The goal is to provide quasi-absolute neutron flux measurements with an accuracy better than 3%. It consists of a double ionization chamber with a Micromegas segmented detection plane and the gaseous pressure can be adjusted to protons – and hence neutron – energy. The sensitivity to gamma and electrons background, the intrinsic efficiency as well as the resolution of this detector have been investigated. [ABSTRACT FROM AUTHOR]

235U and 238U are very important isotopes in the nuclear energy system. Their neutron-induced fission cross sections have been measured intensively and evaluated as standard up to 200 MeV. However, as a matter of fact, the experimental data in the high-energy region are scarce. This work reports the measurement of 235, 238U(n, f) cross sections relative to n-p scattering performed at the China Spallation Neutron Source (CSNS) back-streaming neutron facility (Back-n). Preliminary results of 235, 238U(n, f) cross sections from 10 to 66 MeV are obtained, which are generally following the shape of the IAEA standard. However, significant discrepancies are observed at some given energies, which will be further studied. [ABSTRACT FROM AUTHOR]

Prompt fission neutron spectra (PFNS) are crucial to any neutronic simulation of critical nuclear systems. An experimental setup dedicated to the measurements of PFNS of very high accuracy was developed at the Los Alamos Neutron Science Center (LANSCE) some ten years ago. It allows for the measurement of PFNS for neutron induced fission at the Weapon Neutron Research (WNR) neutron source of the LANSCE. A measurement of the PFNS from the 235U(n,f) reaction was realized recently and is currently analyzed. Preliminary results are presented here and are compared to present nuclear data evaluations. [ABSTRACT FROM AUTHOR]

This is a transcript of my talk for Nuclear Data for Science and Technology conference, ND2022. The talk is available on YouTube: www.youtube.com/watch?v=a%5fWYcTHco00. This work is derived from a 2021 paper I wrote in the American Nuclear Society's journal Nuclear Technology 207, S24 (2021). It was published in a special issue together with twenty-three other papers, for the 75th Anniversary of the culmination of the Manhattan Project. It would be better to watch the video than read this transcript! [ABSTRACT FROM AUTHOR]

The study of fission yields has a major impact on the characterization and understanding of the fission process and its applications. Fission yield evaluations represent the synthesis of experimental and theoretical knowledge in order to perform the best estimation of independent fission yields. Today, the lack of correlations between the different fission observables induces several inconsistencies in the evaluations. Different works proposed to estimate the correlations of the independent fission yields satisfying the consistency to the chain yield evaluations. Nevertheless, none of them introduces a prior correlations of the independent and chain evaluations in the evaluation process. Covariance matrix of fission yields depends on the evaluation method used according to the kinds of existing measurements. The consistency is deeply entangled to the statistical agreement between each dataset considering the covariance of measurements. Moreover, covariance of model parameters does not represent the only contribution to the evaluation covariance matrix. Thus, a new evaluation process is crucial to provide a complete and coherent evaluation file. The LEPh Laboratory of CEA Cadarache is developing this program for the future version of the JEFF-library. [ABSTRACT FROM AUTHOR]

There are several different types of the integral data of nuclear fission systems, and the accuracy of the numerical predictions of them are related with each other via the nuclear data commonly used in the numerical simulations. Thus, it is sometimes possible that measurement data of one type of the integral data are used to improve the prediction accuracy of the different type of the integral data. To quantitatively evaluate such possibility, the similarity of the different types of the integral data is important. In this study, we quantitatively evaluate the similarity between neutron multiplication factors and nuclide inventories during nuclear fuel burnup from the viewpoint of the nuclear data uncertainties using the representativity factors. Using the Burner module of the CBZ reactor physics code system for fuel pin-cell burnup problems, we calculated the sensitivity of the neutron infinite multiplication factors and the inventories of the 17 actinoids at several fuel burnup points. The neutron multiplication factor during the fuel burnup was considered the target parameter for which the prediction accuracy is improved, and the degree of similarity of the nuclide inventory data during burnup to the target was quantitatively evaluated using the representative factor. Subsequently, multiple nuclide inventory data were combined using the concept of the extended bias factor method to create a fictitious parameter, and we investigated how much this fictitious parameter can increase the representativity factor for the target parameter. As a result, the representativity factor for the target parameters could be increased to more than 0.8 using some nuclide inventory data, and up to 0.92 depending on the burnup, even taking into consideration the measurement error. [ABSTRACT FROM AUTHOR]

The covariance evaluation for neutron cross sections in CENDL is briefly introduced in this work. The methodology for evaluation contains the nuclear reaction theoretical model-dependent approach and the non-model dependent one according to the amount of experimental data. Both approaches are based on the Generalized Least-Squares (GLSQ) method. To obtain more reliable uncertainties from experimental measurement, the analysis of the sources of experimental uncertainties (ASEU) is used rigorously in the evaluation. Moreover, machine learning (ML) methods which can deal with the data mining with a more automatic way are employed to evaluate the cross sections in a large-scale nuclear mass region to compensate the uncertainties on some nuclides and reactions, lack of experimental data for, e.g., unstable nuclei and fission products. The covariance files for 70 fission product nuclei are obtained through the model-dependent method in CENDL-3.2, and the covariances for U and Pu isotopes have also been finished with high fidelity, which will be released as part of the next CENDL. [ABSTRACT FROM AUTHOR]

A new evaluation of spectrum averaged cross sections (SACS) of 235U, 238U, and 239Pu measured in the 252Cf(sf) reference neutron field is presented and found to be consistent with the original Mannhart SACS evaluation in IRDF-2002. The comprehensive vetted experimental database that includes SACS ratio and absolute SACS measurements of major actinides is being used to update the SACS database employed as input of the new GMApy code to derive the Neutron Standards. An update of the current neutron standards based on Time Projection Chamber (TPC) shape data, a new comprehensive uncertainty quantification, and revised SACS experimental database is proposed which result in a 0.7% increase of the evaluated 239Pu(n,f)/235U(n,f) crosssection ratio in the 1–5 MeV energy region. The increase is due to a 0.3% reduction of the standard 235U(n,f) cross section and a 0.4% increase of the 239Pu(n,f) reference cross section in the 1–5 MeV energy region. Those changes are well within estimated USU fission cross-section uncertainties of 1.2%, but are relevant for the evaluated mean values. [ABSTRACT FROM AUTHOR]

The prompt fission neutron spectrum (PFNS) from neutron-induced fission is a fundamental quantity for the behavior of nuclear reactors, and has been measured many times on a wide variety of nuclei and covering different ranges of incident and emitted neutron energies. However, results from past measurements are frequently called into question in modern nuclear data evaluations because of a lack of thorough experimental documentation and incomplete uncertainty analyses. The Chi-Nu experiment at Los Alamos National Laboratory was designed to produce high-precision measurements of the PFNS of major actinides over a wide range of incident and emitted neutron energies, and with the documentation and covariance analysis required to ensure that the results of this experiment maintain their impact long into the future, thereby avoiding this pitfall of past measurements. In this work we describe the Chi-Nu experiment along with summaries of the treatment of and methods developed to address two important components of the analysis of Chi-Nu data: random-coincidence backgrounds and MCNP simulations. Furthermore, we describe the first results for correlations not just between all data points collected on a single target nucleus, but also between all data points from separate Chi-Nu measurements on 235U and 239Pu. These correlations are important for accurately calculating ratios of the PFNS from one actinide to another, which are rare and can be informative for nuclear data evaluation efforts. [ABSTRACT FROM AUTHOR]

Fission yields are of major interest for the nuclear industry and the study of the fission process. Fission yields are determined by evaluation process based on the analysis of experimental datasets and completed by phenomenological models. The aim is to provide the best estimation of independent yields of 235U(nth,f) reaction. In this paper, we will focus on the methodology of assessment of the nuclear charge distribution per mass. In the JEFF-3.1.1, the Wahl's parametrization of the Zp-model is used to complete the experimental knowledge. Nevertheless, the lack of this parametrization consists in the absence of uncertainty information. Consequently, it is impossible to generate the components of independent yield correlation matrix from the Zp-model. In this context, we propose to use the Zp model with a new parametrization to assess the charge distributions. Two different calculations have been developed: the first one is based on a Wahl-like linear approximation of the parameters as a function of mass. The second approach consists to apply a "direct-Zp model" without linear assumptions. This analysis is achieved using the Markov-Chain Monte-Carlo (MCMC) method to adjust the model parameters and then to deduce the covariance of charge distributions. Moreover, with our development, we have directly and consistently described the pre-neutron and post-neutron charge distributions. [ABSTRACT FROM AUTHOR]

Fission product yields (FPY) are important for a variety of applications (reactor neutronics, spent fuel, dosimetry, radiochemistry, etc.) and are currently included in many of the evaluated libraries around the world. The FPYs in the current US evaluation, ENDF/B-VIII.0, are mainly based on the 1994 evaluation of England and Rider and have only had slight updates—such as the inclusion of a 2 MeV point for 239Pu—since their development. Additionally, only mean values and uncertainties are included in the evaluation, not full correlations. Los Alamos National Laboratory, in collaboration with several other institutes, has been working on an updated evaluation for the FPYs of 239Pu(n,f), 235U(n,f), 238U(n,f), and 252Cf(sf) using the deterministic, Hauser-Feshbach, fission fragment decay code, BeoH. BeoH calculates the FPYs consistently with many other prompt and delayed fission observables, explicitly taking into account multi-chance fission and ensuring consistency between observables. In addition to providing updated means and uncertainties for the FPYs on a pointwise energy grid from thermal to 20 MeV, we calculate correlations between all FPYs at each incident energy and across incident energies. Here, we discuss the development of these covariance matrices, differences in the correlations between FPYs based on the parameters that are included in the model optimization, and correlations across incident energies for neutron-induced fission. [ABSTRACT FROM AUTHOR]

The fission yield data provided by the evaluated nuclear data files do not contain covariance information, which is not conducive to uncertainty analysis. To generate covariance information, the model parameters of the code GEF which describes the fission process are sampled and the independent fission yield samples are calculated. The covariances of independent fission yields of 235U, 239Pu, and 241Pu thermal neutron-induced fissioning systems are generated individually based on the above samples. This method is verified by comparing the uncertainties of burnup-related responses based on fission yield samples calculated by GEF and based on fission yield samples generated with the covariances. The influence of correlations among fissioning systems is also quantified and the joint covariances among different fissioning systems calculated with GEF are demonstrated correct. In addition, the Bayesian Monte Carlo method is adopted to adjust the model parameters of GEF, and the numerical results prove the effectiveness of the adjustment. [ABSTRACT FROM AUTHOR]

Evaluation of covariance for JENDL was virtually started after the release of JENDL-3.2. The covariance data were obtained for 16 nuclides and compiled to the JENDL-3.2 Covariance File. At the time of the JENDL-4.0 development, covariances were much enhanced especially for actinides; covariance data were given for 99 nuclides in total. The latest version JENDL-5 includes covariance data for 105 nuclides by adding new evaluations for light nuclides and structure materials. An overview of the covariance evaluation for JENDL is presented. [ABSTRACT FROM AUTHOR]

The EUCLID (Experiments Underpinned by Computational Learning for Improvements in Nuclear Data) project created a library of sensitivities for nine different integral responses with respect to nuclear data. These integral responses were obtained from measurements at LLNL (Lawrence Livermore National Laboratory) pulsed spheres, critical and sub-critical assemblies. At the same time, covariances for ENDF/B-VIII.0 were processed at LANL (Los Alamos National Laboratory). The combination of these data allow us to study the impact of nuclear-data covariances on various integral responses, either by forward-propagating covariances via sensitivities, or by using nuclear data, integral responses, and sensitivities for adjustment. Here, we will present: the impact of 1H, 9Be, 12C, 27Al, 56Fe, 235,238U, and 239,240Pu ENDF/B-VIII.0 covariances on simulated bounds of the following integral responses: LLNL pulsed-spheres neutron-leakage spectra, the effective neutron multiplication factor, reaction rates, and reactivity coefficients of ICSBEP critical assemblies. Also, adjustment results with the same nuclear-data covariances and responses will be discussed. LA-UR-22-31309 [ABSTRACT FROM AUTHOR]

The use of games in education is applied in classroom settings from all academic levels. More importantly, games can motivate student learning in courses that depend heavily on evaluation and comprehension. The number of digital games available to enhance learning outcomes while motivating student-learning are overwhelming. Nonetheless, access to such content can be costly and limited to academic institutions that lack funds and technology. In this paper, we analyzed how a set of magnetic spheres paired with games motivated student learning in courses across 2 multicultural classrooms (Physics and Social Studies). By designing a session about the atomic bomb in a history course, professors from both History and Physics used a set of small magnetic spheres and Albert Einstein's equation E=mc2 to complement student learning in a history classroom to comprehend a topic, by using components of the magnetic spheres as an analogy of the nucleus of an atom, where the magnetic force between spheres represents the weak nuclear force. We explained the nuclear fission phenomenon and the history behind this discovery in a more hands-on approach. With this analogy, a game was designed, in which students after having taken a lecture on the history of nuclear fission and an overall explanation of Albert Einstein's formula, simulated building the atomic nuclei of radioactive elements by adding a pair of neutrons to quantify the energy released when separated as individual particles. After completing the game-based activity, we conducted a series of surveys among students to 1) analyze students' perception of the learning process during multidisciplinary classes with classroom games and 2) identify attitudes towards subject comprehension through classroom games. The experiment was carried out in sessions of 50 minutes per group. The participants of the case study were students from a private education institution in the northwestern region of Mexico (State of Sonora). We examined how these game-based activities were perceived by the students regarding their motivation to learn. In order to enhance the motivation for student learning, multidisciplinary collaboration should be included in the design process of the curriculum the school offers to its students. [ABSTRACT FROM AUTHOR]