Conveners
Fission: I
- Amy Lovell (LANL)
Fission: II
- Anton Tonchev
Fission: III
- Marc Verriere
Fission: IV
- Maria Anastasiou (LLNL)
Fission: V
- Lucas Snyder (LLNL)
Fission: VI
- Andrea Mattera (BNL)
Fission: VII
- Denise Neudecker (LANL)
Fission: VIII
- Nicolas Schunck
Fission: IX
- Diego Ramos
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7. New developments in fission studies within the time-dependent density functional theory frameworkAurel Bulgac25/07/2022, 09:30
LA-UR-21-28456
We have extended significantly our description of fission by examining a larger set of observables and more nuclei. We extract neutron and proton numbers of fission fragments, their spins and fission fragments relative orbital angular momentum and their correlations, investigate neutrons emitted at or shortly after scission, excitation energy sharing mechanism, total kinetic...
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Anabella Tudora25/07/2022, 09:54
The influence of fragment distributions (experimental or theoretical) on the prompt emission results deserves a special investigation, as a part of methods and procedures used for the validation of fission fragment distributions. Such investigations are based on the primary model results (which consist of matrices of different prompt emission quantities as a function of fragment A, Z and its...
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Chikako Ishizuka25/07/2022, 10:06
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...
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Kazuki Okada25/07/2022, 10:18
Fission plays an important role in the study of nuclear data in the actinide region. The dynamical approach to fission using the multi-dimensional Langevin equation has been widely accepted as a practical method. In this approach, nuclear shapes are expressed with a few shape parameters and the fission process is described as their time evolution by the Langevin equation. The shape parameters...
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Jingde Chen, Satoshia Chiba25/07/2022, 10:30
We present our first results for a microscopic simulation of symmetric boost fission in terms of the antisymmetrized molecular dynamics (AMD), which incorporates the mean-field effects (as the TDDFT) via SLy4 effective interaction as well as stochastic 2-nucleon collisions similar to the cascade model. Due to these features, AMD is capable of obtaining not only the “expectation value” or...
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Ionel Stetcu25/07/2022, 10:42
Fission fragment properties are set, to a large extent, during the scission process. It is generally assumed that the fully accelerated fission fragments can be treated as compound nuclei, and their de-excitation towards a long-lived state via prompt neutron and gamma emissions can be treated within a statistical model like the Hauser-Feshbach approach to nuclear reactions. Accurate modeling...
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Jorgen Randrup25/07/2022, 11:45
The origin and character of the fission fragment angular momenta are currently topics of intense theoretical study. We describe how the angular-momentum bearing modes of the evolving dinuclear complex are being agitated at different rates by multiple transfers of individual nucleons, the mechanism long understood to be the primary cause of the transport phenomena displayed by damped nuclear...
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Marc Verriere25/07/2022, 12:09
Nuclear fission is the fundamental mechanism that determines energy production in nuclear power plants. Predictive fission models are necessary for national security applications and are also key to explain the relative abundances of the elements in the universe. In the first part of this talk, we present a novel approach based on particle-number restoration techniques in the fission fragments...
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Stefano Marin25/07/2022, 12:21
Following the binary fission process, the two energetic fission fragments radiate their energy and angular momenta in the form of neutron and gamma-ray emission. These electrically neutral particles represent important signatures of fission in non-destructive assay of nuclear material and an analysis of the emitted radiation can be used to characterize the fissioning source. The emission of...
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Olivier Serot25/07/2022, 12:33
Despite the numerous theoretical [1] and experimental [2] works published very recently, the way in which fission fragments acquire their angular momentum is still an open question. This angular momentum generation mechanism is important not only for improving our understanding of the fission process, but also for nuclear energy applications, since fission fragments angular momentum strongly...
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Nicolas Schunck25/07/2022, 12:45
The goal of the FIRE topical collaboration in nuclear theory (2017-2021) was to determine the astrophysical conditions of the rapid neutron capture process (r-process), which is responsible for the formation of heavy elements. This was achieved by including in r-process simulations the most advanced models of fission (spontaneous, neutron-induced, β-delayed) that are beeing developed at LLNL...
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Kazuya Shimada26/07/2022, 06:00
The total kinetic energy (TKE) of fission fragments is accounting for about 80 to 90 % of the Q-value in nuclear fission. Therefore, it is important to understand the characteristics of TKE from the perspective of nuclear energy utilization and basic research, e.g., number of fission in reactor power or local heating of the r-process site including fission recycling. Naively thinking, the TKE...
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Olivier Litaize (CEA)26/07/2022, 06:12
The nuclear de-excitation process (through neutron, gamma and electron emission) simulated by the Monte Carlo code FIFRELIN [1] has been improved recently and compared with results from fission and radiative neutron capture experiments. Several examples will be presented during this conference.
Firstly, the initial goal of the code is to predict fission observables and associated...
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Ana Maria Gomez26/07/2022, 06:24
The particle spectrometer VERDI (VElocity foR Direct particle Identification) allows high-precision measurements of fission fragment (FF) mass distributions by using the 2E-2v technique. VERDI consists of two arms with 16 Silicon PIPS (Passivated Implanted Planar Silicon) detectors and a Micro Channel Plate (MCP) each. The MCPs provide the pick-off signal used to trigger the time-of-flight...
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Zhihao Gao26/07/2022, 06:36
Independent fission yields in neutron-induced fission at high neutron energy is important for the understanding of the fission process, and it is also in relevant for reactor physics applications. So far, measurements of independent fission yields in proton-induced fission has been performed at the IGISOL facility at the University of Jyväskylä, using the Penning trap as a high...
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13. (WITHDRAWN) Simultaneous measurements of prompt fission γ-rays and neutrons with CLLBC detectorsCristiano Lino Fontana26/07/2022, 06:48
The knowledge about prompt neutrons and $\gamma$-rays spectral characteristics in nuclear fission is essential to understand the nuclear de-excitation process of fission fragments [1,2]. Preferably, these observables should be known in correlation with fragment properties like mass and kinetic energy.
Typical multi-parameter experiments require long measurement times and efficient detector...
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Walter Loveland26/07/2022, 09:30
The study of the fast neutron (En = 3-100 MeV) induced fission of actinide nuclei allows us to study the relative role of Coulomb and dissipative forces in a large scale nuclear collective motion. One is aware of the practical applications of knowing the energy release and its dependence on neutron energy and fragment mass. We have been engaged in studies of the total kinetic energy release...
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Matthew Devlin26/07/2022, 09:42
The Chi-Nu project at the Los Alamos Neutron Science Center (LANSCE) continues to measure Prompt Fission Neutron Spectra (PFNS) as accurately and completely as possible, with fully understood uncertainties including uncertainty correlations. These measurements use the LANSCE/WNR white-spectrum neutron beam and cover incident neutron energies from below 1 MeV to 20 MeV, and were originally...
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Ronald Malone26/07/2022, 09:54
Fission product yields (FPY) are an important observable for fundamental and applied nuclear physics. We are conducting a comprehensive study of the cumulative FPY from neutron-induced fission of $^{235}$U, $^{238}$U, and $^{239}$Pu between 0.5 and 15 MeV at the Triangle Universities Nuclear Laboratory. Actinide foils are irradiated using monoenergetic neutron beams produced by a tandem...
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Panagiotis Gastis26/07/2022, 10:06
Independent fission product yields (FPY), i.e., yields of fission products right after the prompt neutron emission, but before beta decay, are an important piece of data for nuclear fission modeling and fission applications. The Spectrometer for Ion Determination in fission Research (SPIDER), was developed at Los Alamos Neutron Science Center (LANSCE) for measuring FPYs from neutron-induced...
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Amy Lovell26/07/2022, 10:18
The Hauser-Feshbach fission fragment decay model HF$^3$D calculates the statistical decay of fission fragments through both prompt and delayed neutron and $\gamma$-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. ...
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Yuval Waschitz26/07/2022, 11:15
Measurements of independent isotopic fission yields (IIFYs) provide access to the underlying probability distribution of products resulting from fission. The knowledge of IIFY distributions contributes to our understanding of the nuclear fission process in more depth with respect to mass yield distributions. A better understating of the fission process has wide implications, including the...
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Anton Tonchev26/07/2022, 11:39
Fission product yields (FPY) are essential ingredients for addressing questions relevant to a range of basic and applied physics. Examples include the cosmic nucleosynthesis processes that created the elements from iron to uranium, decay heat release in nuclear reactors, reactor neutrino studies, radioisotope production, development of advanced reactor and transmutation systems, and many...
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Maria Anastasiou, the NIFFTE Collaboration26/07/2022, 11:51
While nuclear data play an important role in nuclear physics applications, it has become important to have a better understanding and try to minimize their uncertainties. In particular, there is a need for precision neutron-induced fission cross section measurements on fissile nuclei. Neutron-induced fission cross sections are typically measured as ratios, with a well-known standard in the...
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Martin Schulc26/07/2022, 12:03
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 high emission isotopic source with emission...
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Christophe Sage27/07/2022, 06:00
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 yields measurements has been initiated for several years at the LOHENGRIN spectrometer. However, the measurement of very low...
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Pieter Mumm27/07/2022, 06:24
The Alpha-Gamma device at the National Institute of Standards and Technology (NIST) utilizes neutron capture on a totally absorbing $^{10}$B deposit to measure the absolute flux of a monochromatic cold neutron beam to better than 0.1% precision. Gammas produced by the boron capture are counted using high purity germanium detectors, which are calibrated using a precisely characterized alpha...
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Shuichiro Ebata27/07/2022, 06:36
The charge distribution of fission fragments is a significant quantity to estimate and evaluate the neutron emission yields from fission fragments. The distribution has been evaluated as the deviation from the unchanged charge distribution (UCD) assumption in which the fragments keep the neutron-proton ratio of the fissile parent nucleus. The deviation is called the charge polarization...
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Andreas Oberstedt27/07/2022, 06:48
The multi-humped fission barrier is the result of superposing microscopic shell corrections to the macroscopic liquid drop model [1]. A manifestation of that is the existence of shape isomers [2, 3], as observed in several actinide nuclides. However, the - most often - double-humped barrier is much more than just a concept, since it is related to several fission observables. These data may...
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Stephan Pomp (Uppsala University)27/07/2022, 07:45
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Andrea Mattera27/07/2022, 08:09
Isomeric states have been observed in about 150 of the hundreds of isotopes that can be produced in the fission of major actinides. These isomers can be populated directly through fission, and the isomeric yield ratio (IYR) represents the relative population of the excited state(s) and the ground state (GS) independent yield.
Due to the underlying nuclear structure, the isomeric state often...
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Jason Harke27/07/2022, 08:21
Over the past decade a series of measurements have been performed to determine fission product yields from a series of actinides. The National Criticality Experiments Research Center operates several critical assemblies one of which is Godiva. Godiva was operated in burst mode to produce a prompt fission neutron spectrum to fission actinide materials so that their relative yields could be...
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Anthony Ramirez27/07/2022, 08:33
The LLNL-LANL-TUNL collaboration has been providing high-quality fission product yields (FPYs) from neutron-induced fission of $^{235}$U, $^{238}$U, and $^{239}$Pu [1]. Fission products have been measured using activation technique with monoenergetic and pulsed neutron beam produced at the tandem accelerator at the Triangle Universities Nuclear Laboratory (TUNL). The previous campaign...
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Jack Silano27/07/2022, 08:45
The Bohr Hypothesis, one of the most fundamental assumptions in nuclear fission theory, states that the decay of a compound nucleus with a given excitation energy, spin and parity is independent of its formation $^{[1]}$. Using fission product yields (FPYs) as a sensitive probe, we have performed novel high-precision test of the combined effects of the entrance channel, spin and parity on the...
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Diego Ramos27/07/2022, 11:00
The fission process has intrigued physicists for a long time from both, experimental and theoretical points of view~\cite{Bohr,wil76,bro90}. The large deformations achieved in the process and the interplay between intrinsic and collective degrees of freedom prevent, so far, from a complete microscopic description of the phenomenon~\cite{sorting,scamps18,kh18}. The role of the nuclear structure...
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Lucas Snyder (LLNL)27/07/2022, 11:24
The goal of the Neutron Induced Fission Fragment Tracking Experiment (NIFFTE) is to measure fission cross sections with unprecedented precision. The NIFFTE Collaboration has designed and built a Time Projection Chamber (TPC) for this purpose. The tracking capabilities of this device allow for the full reconstruction of charged particles produced by neutron beam induced fissions from a thin...
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Elisa Pirovano, the n_TOF Collaboration27/07/2022, 11:36
The $^{235}$U(n,f) cross section is one of the most important cross-sections in many applications, and it is a standard at the thermal neutron energy point (0.025 eV), and from 0.15 MeV to 200 MeV. Above 100 MeV, it also plays an important role in understanding fundamental nuclear physics processes, as it can be related to the properties of excited nuclear matter. Above 50 MeV, however, the...
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Alice Manna, the n_TOF Collaboration27/07/2022, 11:48
The $^{235}$U(n,f) cross section is one of the most important neutron cross-section standards, and therefore it is recognized as a convenient reference for several other reaction cross-section measurements at thermal energy and between 0.15 MeV and 200 MeV. Outside these energy ranges the cross section is either not well known nor measured yet, as for example above 200 MeV, where evaluations...
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Daniel Fernandez27/07/2022, 12:00
During the last ten years, the use of inverse kinematics in the experimental study of fission is bringing a wealth of new observables obtained in single measurements, which allows their analysis and, also importantly, of their correlations [1, 2]. An ongoing application of this technique the basis of a series of experiments performed with the variable-mode, large-acceptance VAMOS++...
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José Luis Rodríguez Sánchez (Universidad de Santiago de Compostela)27/07/2022, 12:12
Fission reactions investigated in inverse kinematic at relativistic energies have proven
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to be a powerful technique to get access to a large variety of non stable heavy nuclei
[1] but also to fully identify, for the first time, in atomic and mass number both fission
fragments [2]. These systematic investigations made possible to establish the role of
proton shells in the asymmetric fission... -
Audrey Chatillon28/07/2022, 06:00
The anatomy of nuclear fission - a complex many-body process that has challenged precise modeling for decades - is explored via a comprehensive inverse-kinematics experiment. A Coulomb-fission measurement of relativistic $^{234,235}$U and $^{237,238}$Np projectiles at the GSI, using the R3B/SOFIA setup [1,2,3,4], was performed to identify on an event-by-event basis, in terms of their mass and...
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Tobias Wright, the n_TOF Collaboration28/07/2022, 06:24
The average energy and multiplicity of prompt $\gamma$-rays from near thermal neutron induced fission of $^{235}$U have been measured using the STEFF detection setup at both the high-flux ILL research reactor and the neutron time-of-flight facility n_TOF. As highlighted by the NEA High Priority Request List, these quantities are of importance to the heating of non-fuelled elements of a...
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Nathan Giha28/07/2022, 06:36
Heavy nuclei toe a delicate balance between the attractive strong nuclear force and the repulsive Coulomb force. When this balance is disrupted in favor of the Coulomb force, heavy nuclei may elongate and fission into two fragments. Fission was first observed over eighty years ago and theoretically explained shortly thereafter. We now know that good macroscopic and microscopic fission models...
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Dan Mihai Filipescu28/07/2022, 06:48
Photofission and photoneutron reactions on $^{238}$U and $^{232}$Th were investigated in the energy range of 5.86 MeV – 20.12 MeV by quasi-monochromatic $\gamma$-ray beams produced in laser Compton-scattering at the NewSUBARU synchrotron radiation facility. Direct neutron-multiplicity sorting was performed with a flat-efficiency neutron detector [1]. Following Terrell’s prescription [2], a...
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Denise Neudecker28/07/2022, 07:00
LA-UR-21-29120
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Historically, there is little to no consistency between the various types of nuclear fission data in our libraries (Patrick Jaffke, NSE 190, 258 (2018)), despite the fact that we know these observables to be correlated through the joint fission process underlying them all. For instance, the energies and multiplicities of prompt neutrons and gamma rays are correlated through the... -
Todd Bredeweg
Fission product chain yields were historically determined by chemical separation and beta counting of fissile samples irradiated in carefully controlled fission chamber experiments$^{1,2}$. These measurements provided the means to extract absolute fission product yields (yield per fission, or $Y_i/f$ for the $i^{th}$ fission product) that are included in the international nuclear data...
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Matthew Gooden
Under a joint collaboration between Los Alamos National Laboratory, Lawrence Livermore National Laboratory and the Triangle Universities Nuclear Laboratory, a set of absolute cumulative fission product yield measurements has been performed. The energy dependence of a number of cumulative fission product yields (FPY) have been measured using quasi-mono-energetic neutrons for three actinide...
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Paola Marini
Prompt neutron emission is a challenge in nuclear fission research. Accurate values of the number of prompt fission neutrons emitted in fission reaction and their kinetic energy distributions are essential for fundamental and applied nuclear physics. Indeed, they provide valuable information on the amount of excitation energy of the heated fissioning system transferred to the primary...
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Ali Al-Adili
The neutron emission is an important fingerprint of the excitation-energy sharing in the nuclear fission process. Highly excited, neutron-rich nuclei release their energy by emitting prompt neutrons and γ-rays. Improved determination of particle-emission characteristics enhances the understanding of fission dynamics. The nuclear data libraries lack data which are crucial for various...
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Vanessa Linero
The scarcity of independent yields for Pu-239 at fast neutron energies hinders the ability to properly generate a predictive model and requires additional measurements for proper simulations. Obtaining independent yields can be difficult, as the measurement of short-lived fission products places a time constraint on detection methods available. The use of a monoenergetic neutron beam and rapid...
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Cristian Massimi
The neutron time-of-flight facility n_TOF at CERN has been producing relevant nuclear data for science and technology since 2001. In particular, neutron-induced cross sections have been reported on more than 100 reactions, so far. Among them, the $^{235}$U(n,f) cross section was deeply studied [1,2] in different energy regions and using several detector concepts, for instance Parallel Plate...
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Satoshi Chiba
There are numerous ways to treat theoretically nuclear fission, ranging from pure phenomenology, macro-micro method to purely microscopic ones. In this talk, we will concentrate on a macro-micro method in terms of the Langevin equations. In this method, time-evolution of the positions and momenta of shape degree of freedom is treated as a coupled first-order stochastic differential equations...
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