Low-energy nuclear reaction mechanisms are frequently classified as either direct, pre-equilibrium or compound nucleus ones. Here, the role of the first two of these is examined up to the stage of the formation of a compound nucleus. Although direct reactions are often distinguished from pre-equilibrium ones, the point of view is adopted here that the latter consist, for the most part, of a...
A nucleus is a good stage to study a many-body quantum system in nature. Excited nuclei generate a variety of vibrations, rotations, and so on, which are called nuclear collective motions. It is known that the leading-order effect of nuclear vibrational excitations is 1-particle 1-hole (1p1h) states. With increasing the excitation energy, higher-order correlations beyond 1p1h states become...
The nucleon-nucleus optical potential (OP) is one of the essential ingredients in both direct and compound reaction calculations. Phenomenological parametrizations based on fits to elastic scattering data are widely used for many applications in astrophysics, basic nuclear science, and nuclear data. However, the explicit connection of the OP with the underlying nuclear structure has always...
This work presents the current state of a consistently developing dispersive Lane-consistent coupled channels optical model. The model considers the optical potential of a soft deformed target nucleus as an axially deformed potential with linear corrections corresponding to the softness and non-axiality of a nucleus [1]. A soft rotator model was used to calculate the "effective" deformations –...
Description of the deuteron-nucleus interaction is still a challenge for the basic research, while the accurate activation cross sections are highly requested by several on-going strategic research projects (ITER, IFMIF, SPIRAL-2). Actually, evaluation of the deuteron-induced activation data for IFMIF has pointed out a ratio of ~70 for the deuteron- and neutron-induced activities over the same...
Cross sections for compound-nuclear (CN) reactions are important for nuclear astrophysics and other applications. Direct measurements are not always possible for the reactions of interest and calculations without experimental constraints can be quite uncertain. Thus indirect approaches, such as the surrogate reaction method (SRM), are being developed to fill the gaps. The SRM, which uses a...
Understanding neutron-induced reaction rates on rare isotopes is important in fission and nucleosynthesis processes and applications in nuclear energy and forensics and stewardship science. Informing these rates requires indirect methods and rare isotope beams. The Surrogate Reaction Method (SRM) [1], where beams interact with light-element targets, has been demonstrated [2] as a valid...
For better understanding of reaction rates for radioactive isotopes relevant for the nu-p process, we directly measured cross sections of $^{56,59}$Ni(n,p), $^{56}$Co(n,p), and $^{59}$Ni(n,$\alpha$) using the LENZ (Low Energy NZ) instruments at the Los Alamos Neutron Science Center (LANSCE). I will discuss the impacts of updated experimental reaction rates in the nu-p process nucleosynthesis...
Optical potentials remain an indispensable ingredient for modeling many types of nuclear reaction, such as in statistical (Hauser-Feshbach) calculations of radiative capture. As with level densities and γ-ray strength functions, optical potentials for systems near the neutron dripline remain poorly known but are important for characterizing key astrophysical nucleosynthesis pathways. Recent...
With very few exceptions, direct measurements of neutron capture rates on radionuclides have not been possible. A number of indirect methods have been pursued such as the surrogate method [1], the γ-ray strength function method [2,3], the Oslo method [4-7] and the β-Oslo method [8]. Substantial effort has been devoted to quantify the usually large systematic errors that accompany the results...
Neutron induced reactions remain as a subject of great interest for both theory and applications, especially at medium energy range (20 MeV - 40 MeV), where particle emission is mostly described by “pre-equilibrium processes” and nuclear structure effects start to wash out. The current theoretical nuclear models still lack the capability to predict cross sections for any nucleus in an...
Nuclear reactions on unstable fission products are of interest to nuclear non-proliferation efforts and basic science. While these reactions have historically been extremely difficult to measure, new experimental facilities are beginning to make beams of fission products available for the first time, enabling exciting experiments. The opening of this new area of the nuclear chart for...
The process of spontaneous or induced fission, by which an atomic nucleus breaks into two or more fragments, presents, more than eight decades after its discovery, a very interesting research topic in the field of low- and medium-energy nuclear physics. From a modern perspective, nuclear fission can be considered a representative example of large-amplitude collective motion in a self-bound...
In recent times, new theoretical and experimental results made it clear that the generation and dynamics of fission fragment (FF) intrinsic spins and their correlations were not well understood. During this period, we investigated various aspects of FF spins for compound nuclei 236U, 240Pu, and 252Cf using time-dependent density functional theory (TDDFT) extended to superfluid systems. We...
Accurate nuclear data (ND) are necessary for the conception, development, optimization, and safety evaluation of nuclear energy applications (both fission and fusion) and non-energy applications such as radiation protection, radionuclide production, health, geosciences, space research, security, and industry.
In Europe, the ND activities have been funded so far by national funding agencies...
For detailed technical designs and safety evaluations of innovative nuclear reactor systems, accurate cross-sections are required. Especially, in the field of nuclear systems such as the transmutation of radioactive waste and various innovative reactor systems, neutron-capture cross sections of minor actinides (MAs) and long-lived fission products (LLFPs) are quite important to estimate the...
China Spallation Neutron Source (CSNS) is a newly built large scale facility in 2018. It is generating neutrons by bombarding 1.6 GeV protons into a tungsten target for multidisciplinary research. A back-streaming neutron beamline (Back-n) at CSNS is built at the reverse direction regarding to the proton beam mainly for the nuclear data measurement. Back-n is characterized by its wide energy...
Neutron inelastic scattering is an important process involved in many applications but also for background studies supporting more fundamental research area. In the fast energy range, it is one of the major nucleon-nucleus interactions and its cross section constantly increases above the threshold energy of the first excited state up to a few MeV. In the field of nuclear energy applications or...
Measurements are routinely performed at the Rensselaer Polytechnic Institute (RPI) Gaerttner Linear Accelerator (LINAC) Center to generate nuclear data for different neutron reactions in multiple energy ranges. These measurements use neutrons generated by a 60 MeV pulsed electron LINAC and various neutron and gamma detection systems at different flight path lengths. A new project was...
Capture-to-fission cross section ratios are used as an alternative to absolute cross section measurements. This is due to the simplification on the calculations and the reduction of the uncertainties with respect to an absolute measurement of the cross section by eliminating experimental complications like self-absorption, beam/target overlap and non-uniformities. Different capture-to-fission...
The NEA/OECD included the cross-section of neutron capture and neutron-induced fission reactions for $^{239}$Pu in its High Priority Request List, in response to the demands for more accurate and reliable nuclear data essential for the design and operation of nuclear technologies. Recent efforts have been concentrated on meeting these data needs by means of a new measurement utilizing...
The neutron time-of-flight facility, n_TOF, at CERN, offers the possibility to study neutron-induced reactions thanks to the extremely wide neutron energy spectrum available in its experimental area, from thermal up to GeV. Already since the year 2001, the n_TOF Collaboration has been producing relevant nuclear data for fundamental nuclear physics, technology and astrophysics.
In...
The presentation presents a part of the work carried out in the research contract No. 24284 titled “accuracy evaluation of available fission yield data and updating” under the umbrella of the Coordinated Research Project (CRP): “updating fission yield data for applications” organized by the International Atomic Energy Agency (IAEA). One of the main objectives of this project is to evaluate the...
Neutron-induced reactions on chlorine isotopes have recently been analyzed in a Hauser-Feshbach framework at Los Alamos National Laboratory. Particular focus has been applied to the "fast" energy range above 100 keV, where these reactions become important for applications like CLYC detector characterization and the development of molten chloride fast reactors (MCFRs). However, challenges to...
Photonuclear reaction cross-section data are required for wide-range applications, such as electron accelerator shielding design and possibly nuclear transmutation. So far, the nuclear data libraries, such as JENDL [1], TENDL [2], and ENDF [3], of various target materials have been prepared up to a photon energy of 200 MeV. To establish the libraries, almost all evaluations have been conducted...
We have optimized the optical model potential (OMP) parameters for nucleons (protons and neutrons) induced reaction on 40Ca using the OPTMAN code [1] available on the RIPL-3 data library [2]. The potentials, geometrical and nuclear deformation parameters were extracted via fitting angular distribution data for protons/neutrons elastic and inelastic scattering (Ep,n = 0 – 200 MeV) taken from...
Scattering kernels are more complicated to evaluate than absorption processes due to the fact that scattering procedures involve not only the internal structure of the target nuclei but also the free “classical” particle interacting and emitted from the target. Strictly speaking, the interaction within the nucleus is based on quantum mechanical considerations whereas the emitted particle...
Decay properties of nuclear states in the domain of high nuclear level density (NLD) are usually described within the statistical model of the nucleus using the NLD and photon strength functions (PSFs). In some nuclei with mass $A\sim 30-100$, the NLD might still be insufficiently low even near the neutron separation energy $S_n$. Despite this, the statistical model is used to describe the...
Authors: Miodrag Krmar 1, Rade Smolović 1 , Nikola Jovančević 1
1 Faculty of Science, University of Novi Sad, Novi Sad, Serbia
The cross section values for the 209Bi(γ,xn) nuclear reactions are calculated using the different models for the level density and the radiation strength function by the TALYS code [1]. Based on the obtained data, the yields of nuclear reactions are determined....
Electromagnetic response of the nucleus is characterized by level density and photon strength functions – two key ingredients for modeling statistical gamma decay. Knowledge of these quantities is crucial for our understanding of neutron capture reactions occurring in stars, responsible for nucleosynthesis of heavy elements. The so-called pygmy resonance in photon strength function has emerged...
We derive the fully self-consistent quasiparticle random-phase
approximation (QRPA) equations with noniterative finite amplitude
methods and calculate the transition strengths of giant resonances.
Then, we apply the QRPA results to both neutron radiative capture
calculations based on the statistical Hauser-Feshbach theory and
inelastic scattering calculations based on distorted-wave...
Among the prospective nuclear reactor-produced radionuclides, ytterbium-175 (175Yb) is found to be suitable for the preparation of therapeutic radiopharmaceuticals due to its decay characteristics (T1/2 (4.18d), Emax (480 keV)). It is an important metal that belongs to the rare earth metal family. However, a major constraint for its production via the (n, γ) reaction is the presence of...
With the syntheses of elements up to oganesson (Z = 118), all the fusion evaporation reactions using the 48Ca beams on deformed actinide targets have already been performed. Due to the lack of target material beyond the californium, the use of 50Ti, 51V, and 54Cr is now becoming mandatory to access elements beyond the oganesson (Z = 118). In the SHE mass region, these beams have only been used...
The R-matrix formalism provides an elegant tool for the description of resonant reaction cross sections. Albeit not microscopically based it is widely used because it satisfies conservation rules and yields consistent sets of reaction cross sections. However, R-Matrix theory is limited to two-body channels, while approximations are frequently required for the description of capture and breakup...
Modern time-dependent density functional theory (TDDFT) codes (see e.g. [Comput. Phys. Commun. 229, 211 (2018)][1]) can be used to describe the excited states of nuclei via a number of reaction mechanisms: Through external multipole field excitation, Coulomb scattering, as fission fragments, in heavy ion collisions from around the Coulomb barrier up to deep-inelastic regimes, and via...
In this study, we utilized the Total Monte Carlo (TMC) methodology to simulate the de-excitation process of primary fission fragments in GEF and TALYS. Our primary goal was to establish a framework for evaluating model deficiencies and parameter sensitivities in fission models. As a proof-of-principle we systematically varied the input fission fragment data in TALYS using the GEF code,...
To synthesize a new superheavy element, Z=119, the RIKEN Nishina Center (RNC) upgraded the existing heavy ion linac system (called RILAC) by partially replacing the superconducting linear accelerator (SRILAC) to increase the final beam energy from 5.5 MeV/u to 6.5 MeV/u, enabling a hot fusion reaction of 51V+248Cm. The new Superconducting Electron Cyclotron Resonance Ion Source (SC-ECRIS),...
Plutonium isotopes are produced in nuclear reactors by neutron-induced fission of 235,238U nuclei and by (n,2n), (gamma,n) processes of Neptunium isotopes. Among the Plutonium isotopes, 236Pu nucleus is a trace element of interest for studies of the environmental impact of fuel cycles. Development of new type of fast neutron nuclear reactions destined for scientific researches based on 237Np...
Transmission coefficients describe the probability that a micro-particle will pass through a potential barrier. Using a quantum mechanical approach, the reflection factor is used to calculate the transmission coefficients for charged and neutral particles. Logarithmic derivative is calculated using a rectangular potential in the internal region. With a computer code developed by the authors,...
The properties of nuclear excitations, particularly collective excitation modes such as the giant resonance (GR) and pygmy resonance (PR), can reveal important characteristics of the underlying nuclear structure. The successful description of the nuclear excitations will enable the complete modelling of transitions between their ground and excited states and, furthermore, produce inputs for...
The reason for studying the neutron capture reaction on the mono-isotopic element thulium is twofold. Its only stable isotope, $^{169}$Tm, is often used as a neutron-flux activation monitor. The neutron capture cross-section in the relevant energy range has been measured several times [1-4] in the past and more recently at CSNS [5]. While these data show rough agreement, there are...
History, development and main achievements in sixteen years of the Neutron Activation Analysis based method used for the establishment of the nuclear database at CNESTEN Morocco.
Hamid. Bounouira1*, Hamid. Amsil1, Abdessamad. Didi1, Iliasse. Aarab1, and Abdelwahab. Badague1
1 National Center of Energy, Sciences and Nuclear Techniques (CNESTEN), Morocco
*E-mail: bounouira2000@gmail.com...
V. Alcayne1, D. Cano-Ott1, E. González-Romero1, T. Martı́nez1, E. Mendoza1, A. Pérez de Rada Fiol1, A. Sánchez-Caballero1, J. Balibrea-Correa2, F. Calviño3, R. Capote4, A. Casanovas3, C. Domingo-Pardo2, J. Lerendegui-Marco2 and the n_TOF collaboration.
1 Centro de Investigaciones Energéticas Medioambientales y Tecnológicas (CIEMAT), Spain
2 Insituto de Fı́sica Corpuscular, CSIC -...
The first measurement of 91Zr(n,a)88Sr reaction cross sections [1], performed in the 3.9–5.3 MeV incident–energy range, followed the need of reliable nuclear data for the isotopes of zirconium used in the blanked and first wall of fusion reactors while the related evaluated data changed by up to 6.4 times were found in widely used libraries. The alpha-particle optical model potential (OMP) was...
Porter-Thomas fluctuations of neutron widths are known to skew compound nuclear decay probabilities away from their statistical, Hauser-Feshbach values. For Hauser-Feshbach codes, the common remedy is to apply the width-fluctuation correction factor of Moldauer, or similar, which accounts for correlations between the entrance and exit channels. For more exotic reactions like beta-delayed...
The VElocity foR Direct particle Identification (VERDI) is a fission-fragment spectrometer based on the detection of velocities as well as energies of fission fragments (2E-2v method). It aims at determining fission yield mass distributions with a resolution of at least A/$\Delta$A = 100. VERDI includes two time-of-flight (TOF) sections, each equipped with a micro-channel plate (MCP) and up to...
One of the challenges of nuclear astrophysics is understanding the observed abundances of the p-process nuclei. Nucleosynthesis simulations typically employ an extended reaction network involving tens of thousands of reactions and thousands of isotopes. As it is impossible to directly measure such a vast number of reactions, simulations rely heavily on calculated cross-sections derived from...
When a negative muon stops in matter, it is captured into an atomic orbit, and subsequently, it is captured by the atomic nucleus at a certain probability through the weak interaction [1]. This process is known as muon nuclear capture ($\mu$NC). In this process, most of the muon's rest energy is carried away by a muon neutrino and the remainder is used to excite the residual nucleus. This...
The National Ignition Facility (NIF) laser at Lawrence Livermore National Laboratory is capable of producing a plasma environment with temperatures ~10 keV, particle densities ~1032 m-3, and neutron fluxes of up to 1034 m-2 s-1. These features, combined with the advanced x-ray, neutron and radiochemistry diagnostics that are available at...
In the reactions induced by weakly bound, tightly bound heavy ions and radioactive ion beams, Incomplete fusion (ICF) dynamics has been an issue of prime interest among nuclear physicists over past decade. The studies with projectiles having alpha structure like 12C, 16O and 20Ne has established the onset of ICF dynamics at energy as low up to Coulomb barrier. Exclusive entrance channel...
Nuclear reaction models, and in particular compound nucleus reactions, require the knowledge of nuclear level densities (NLDs), among other ingredients. For decades, analytical expressions have been used in nuclear reaction codes, due to the freedom they offer to the user to modify their associated parameters in order to fit cross sections.
The development of computational resources has...
All level density models currently used in nuclear reaction codes are based on experimental data on absolute values of nuclear level density which are basically coming from two data sets: discrete level scheme at low excitation energies and the s-wave neutron resonance spacing (D0) at the neutron separation energy. These data are known in very limited ranges of excitation energies and spins....
We employ a new method to extract the level densities of neutron-rich isotopes by utilizing (n,p) and (n,$\alpha$) reactions and the evaporation technique to analyze the emitted particle spectra. This level density extraction method is particularly suited to nucleosynthesis at low neutron exposures that typically proceeds by neutron captures along a path extending within a few neutrons away...
The present contribution will give an overview of the photon strength function models developed to compensate for the lack of data for experimentally non-accessible nuclei. During this overview, phenomenological and microscopic approaches will be presented in light of their respective strengths. We will discuss more particularly the added value of microscopic approaches and the progressive...
The photon strength functions (PSFs) and nuclear level density (NLD) are vital ingredients for the calculation of the photon interaction with nuclei, in particular, the reaction cross sections via the Hauser-Feshbach approach [1]. These cross sections are important, especially in nuclear astrophysics [2,3] and in the development of advanced nuclear technologies [4,5].
The role of the...
This presentation brings into focus $^{78,80}$Kr($\gamma$,$\gamma$’), $^{93}$Mo($\gamma$,n) and $^{90}$Zr($\gamma$,n) cross section measurements carried out using real photons at the H$\gamma$GS/TUNL facility. The overarching physics motivation for these experimental investigations is to advance knowledge on a forefront topic in nuclear astrophysics – the nucleosynthesis beyond Fe of the...
I present first experimental evidence for a low-energy toroidal electric dipole mode in the nucleus $^{58}$Ni based on a combined analysis of high-resolution (p,p’), (γ,γ’) and (e,e’) experiments [1]. Large transverse electron scattering form factors are identified as a unique signature of the toroidal nature of E1 transitions. Although $^{58}$Ni is a nucleus with N ≈ Z, these results bear...
Photons provide a particularly clean probe for studying a wide range of nuclear structure phenomena [1]. Their interaction with the nucleus is described by the electromagnetic interaction, so that the nuclear response can be separated almost model-independently from the details of the reaction mechanism. Thus, photon-induced reactions are important tools in nuclear physics for determining the...
The pygmy dipole resonance (PDR) is a feature commonly appearing in the low-lying electric dipole response of nuclei on top of the tail of the giant dipole resonance (GDR). Despite the ongoing debates regarding its origin, its emergence is commonly associated with the presence of the neutron excess and might potentially affect the neutron-capture rates and, thus, abundances of elements...
The vortex photon beam induced nuclear reaction is studied. The interaction formalism of nuclei with vortex photons is developed and incorporated into the statistical reaction model to calculate reaction cross-sections. For 138 nuclei of high nuclear astrophysics and structure interest, the cross-sections of γ-ray emission and neutron production from the decay of the giant resonances (GR)...
This talk will discuss the application of phenomenological R-matrix methods to problems in light nuclei. An overview of the theoretical approaches will be presented and contemporary computer codes will be reviewed. Included here will be a discussion why R-matrix methods are often the method of choice for nuclear cross section evaluations in light nuclei. Examples of current interest to nuclear...
Description of quantum many-body dynamics is extremely challenging on classical computers, as it requires taking into account many degrees of freedom. In nuclear physics, this translates on a large number of break up channels that have to be taken into account depending on the energy of the reaction. Even using classical computing exascale capabilities will not allow a full description of...
The role of angular momentum in fission has been the subject of intense recent attention. Published data showed that, while the fission fragment spins may be generated by highly correlated processes, the final, measured, fragment spins appeared to be largely uncorrelated. This talk will summarize advances made with the fission simulation model FREYA to study the role of angular momentum in...
A simple semi-classical treatment of photon cascades has been developed. The basic assumption is that a nucleus with a classical spin vector J can be represented by the maximally aligned quantum state |J,M = J> with the quantization axis being the spin direction J/J. It is furthermore assumed that a photon emission yields a daughter state of a similar form, |J′,M′ = J′>,...
The mechanism generating fission fragments’ large angular momenta is still a heavily discussed question in nuclear physics. Since they are not directly measurable, experimentally accessible observables are used to derive the angular momenta using nuclear model codes. One of these observables is the ratio between the yields of spin isomers produced in a fission reaction, the so-called isomeric...
As a former student and long-time collaborator of Eric Bauge, I am honored to discuss the advancements in microscopic reaction models aimed at enhancing the reliability of nuclear data. Eric Bauge’s work has been instrumental in fostering close collaborations between nuclear structure physicists and reaction physicists. His encouragement and guidance have inspired me and many others to pursue...
A short overview of the interaction with Eric within the RIPL project will be given. Calculations performed with the semi-microscopic Lane-consistent folding model (SMOM) potential of Bauge et al. [1] extended to coupled channels [2] will be compared with dispersive coupled-channel optical model potentials for 232Th and 238U [3,4].
References
(1) E. Bauge, J. P....
In this talk in honor of Eric Bauge’s leadership in nuclear data collaborations, I describe the CIELO international collaboration that we ran, from 2013-2018. I set this up through the auspices of the OECD/NEA/WPEC in 2013, with much help from Eric. Numerous labs from the US, Europe and Asia collaborated on new measurements and new evaluations. The results of the collaboration positively...
The past couple of decades have seen tremendous advances in nuclear structure and reaction theory. Innovative theory frameworks for describing the nuclear many-body system, increasingly powerful computers, and opportunities for confronting theory predictions with data on unstable nuclei, have been driving the field. An important goal is to move from phenomenological ingredients in reaction...
For more than a decade CEA Bruyeres-le-Chatel and LANL theoretical division have been cooperating on the development of nuclear theories and their application to the nuclear data. Dr. Eric Bauge of CEA had vigorously participated in the collaborative efforts to promote ideas in fundamental theoretical physics to the basis of scientific and/or technological achievements in the applied area. Our...
Most neutron cross section measurements are made relative to cross sections that are referred to as the Neutron Data Standards (NDS). The conversion to absolute cross sections requires precise knowledge of the NDS, as any bias or uncertainty in the NDS will impact the quality of the resulting absolute cross sections. Moreover, the NDS uncertainties constitute a lower limit for these absolute...
Fission cross-sections are crucial in understanding nuclear reactions, for instance, in designing and analyzing nuclear reactors, applications in nuclear criticality safety, etc.
Current challenges stem from inherent biases and uncertainties within existing fission models, limiting their predictive capabilities, and unknown systematic biases in experimental data. For model predictions we...
Neutron and gamma induced reaction data are the important elements in diversified nuclear applications. The complete nuclear reaction information includes the nuclear reaction cross sections, angular distributions, energy spectrum et al. The study of nuclear reaction data and the relevant covariance in China have been carried out for decades under the joint collaboration of China Nuclear Data...
We will briefly summarize changes in the EMPIRE code since the last CNR meeting in 2018. Then we will discuss the fundamental issue of gradual absorption in the Multistep Compound mechanism that has been hindering its use in evaluation work. A new attempt at solving the problem will be presented. We will also mention the advanced treatment of gamma emission in the MSC that, albeit implemented...
We have developed a specialized web application with the purpose of managing, querying, and visualizing Photon Strength Function (PSF) data. This data is compiled in a well-defined format as an outcome of an IAEA Coordinated Research Project [1]. This web application represents a significant advancement in accessibility and interaction with the data over existing platforms, particularly...
