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International audience; The necessary improvement of evaluated nuclear data for nuclear applications development is possible through new and high-quality measurements, often combined with appropriate nuclear-reaction modelling. In particular, improving inelastic cross-section evaluations requires new and high-quality data. We measure (n, n’γ) cross-sections using prompt γ-ray spectroscopy and neutron energy determination by time-of-flight. To extract, from these partial data, the total inelastic cross-section, we rely on theoretical model as well as nuclear structure data such as γ ray emission probabilities. This structure information, tabulated in databases, comes with uncertainty. This directly affects the precision of our results, regardless of how good the measurement is. In this paper, we will present the issue of limited precision structure data and its impact on nuclear reaction data quality in the case of neutron inelastic scattering measurements. We will also discuss how to foresee and mitigate the issue.

GRAPhEME is a γ-spectrometer developed by CNRS/IPHC Strasbourg (France), in collaboration with EC-JRC Geel (Belgium) and IFIN-HH Bucharest (Romania). With its 6 High Purity Planar Germanium detectors and one fission chamber, GRAPhEME, installed at the EC-JRC GELINA facility, was optimized for measurements of accurate (n, xnγ) cross sections on actinides. The experimental methodology is based on the prompt γ-ray spectroscopy coupled to time-of-flight measurements. In this paper, we present an overview of fifteen years of experiments with GRAPhEME at EC-JRC GELINA facility, illustrated by main achievements to highlight the performances reached by our spectrometer. Beyond the experimental work, a close collaboration with theoreticians has emerged allowing the use of the data produced with GRAPhEME to test and constraint nuclear reaction codes like TALYS, CoH and EMPIRE. In a near future, GRAPhEME will be available to start measurement campaigns at the new neutron beam facility SPIRAL2/NFS. There, studies of (n, 2n) and (n, 3n) reactions will be possible and will complete the work done at EC-JRC GELINA on (n, n ) reactions. Despite the amount of cross section data provided by GRAPhEME up to now, the prompt γ-ray spectroscopy method presents some weaknesses that our collaboration tries to overcome. This goes through new calculation schemes based on theoretical modeling constrained on experimental data to infer the total (n, xn) cross section, new instrument to measure conversion electrons but also by being proactive in dissemination activities to make the nuclear structure community aware of our needs about new accurate nuclear structure information on actinides.

Fission barriers for a large number of nuclei have been extracted from Gogny D1M potential energy surfaces and compared to experimental data. The same data have been used to estimate spontaneous fission half-lives on the basis of the least-action path. An upgraded version of the SPY model for the calculation of the main observables related to fission fragments is also presented. Fission path and yields are key ingredients to estimate the composition of matter synthesized by the r-process nucleosynthesis in the ejecta of binary neutron star mergers., SCOPUS: cp.p, info:eu-repo/semantics/published

Premiere partie d’un ensemble de deux articles exposant le processus d’evaluation des donnees nucleaires, cet ensemble presente l’etat actuel de la connaissance theorique des phenomenes de physique nucleaire mis en jeu. Lors de l’evaluation, la connaissance theorique et experimentale est condensee et synthetisee dans des fichiers informatiques utilises par les codes de simulation. Apres un survol du contenu des fichiers evalues, nous decrivons les differentes methodes utilisees pour l’evaluation des donnees nucleaires. Nous exposons particulierement leur modelisation. Des exemples tires de la pratique quotidienne de l’evaluation sont presentes.

The joint evaluated fission and fusion nuclear data library 3.3 is described. New evaluations for neutron-induced interactions with the major actinides U , U and Pu , on Am and Na , Ni , Cr, Cu, Zr, Cd, Hf, W, Au, Pb and Bi are presented. It includes new fission yields, prompt fission neutron spectra and average number of neutrons per fission. In addition, new data for radioactive decay, thermal neutron scattering, gamma-ray emission, neutron activation, delayed neutrons and displacement damage are presented. JEFF-3.3 was complemented by files from the TENDL project. The libraries for photon, proton, deuteron, triton, helion and alpha-particle induced reactions are from TENDL-2017. The demands for uncertainty quantification in modeling led to many new covariance data for the evaluations. A comparison between results from model calculations using the JEFF-3.3 library and those from benchmark experiments for criticality, delayed neutron yields, shielding and decay heat, reveals that JEFF-3.3 performes very well for a wide range of nuclear technology applications, in particular nuclear energy., Acknowledgements The authors would like to thank all contributors to the JEFF project that shared their insights and provided their specific input for the present JEFF-3.3 evaluation and its immediate predecessors JEFF-3.2 and JEFF-3.1.2.

The γ-ray strength function (γSF) is a nuclear quantity that governs photoabsorption in (γ, n) and photoemission in (n, γ) reactions. Within the framework of the γ-ray strength function method, we use (γ, n) cross sections as experimental constraints on the γSF from the Hartree-Fock-Bogolyubov plus quasiparticle-random phase approximation based on the Gogny D1M interaction for E1 and M1 components. The experimentally constrained γSF is further supplemented with the zero-limit M1 and E1 strengths to construct the downward γSF with which (n, γ) cross sections are calculated. We investigate (n, γ) cross sections in the context of astrophysical applications over the nickel and barium isotopic chains along the s-process path.

Photon strength functions describing the average response of the nucleus to an electromagnetic probe are key input information in the theoretical modelling of nuclear reactions. Consequently they are important for a wide range of fields such as nuclear structure, nuclear astrophysics, medical isotope production, fission and fusion reactor technologies. They are also sources of information for widely used reaction libraries such as the IAEA Reference Input Parameter Library and evaluated data files such as EGAF. In the past two decades, the amount of reaction gamma-ray data measured to determine photon strength functions has grown rapidly. Different experimental techniques have led to discrepant results and users are faced with the dilemma of which (if any) of the divergent data to adopt. We report on a coordinated effort to compile and assess the existing experimental data on photon strength functions from the giant dipole resonance region to energies below the neutron separation energy. The assessment of the discrepant data at energies around or below the neutron separation energy has been possible only in a few cases where adequate information on the model-dependent analysis and estimation of uncertainties was available. In the giant dipole resonance region, we adopt the recommendations of the new IAEA photonuclear data library. We also present global empirical and semi-microscopic models that describe the photon strength functions in the entire energy region and reproduce reasonably well most of the experimental data. The compiled experimental photon strengths and recommended model calculations are available from the PSF database hosted at the IAEA (http://www-nds.iaea.org/PSFdatabase)., SCOPUS: re.j, info:eu-repo/semantics/published

Photoneutron cross sections were measured for $^{137}$Ba and $^{138}$Ba at energies below two-neutron threshold using quasi-monochromatic $\gamma$-ray beams produced in laser Compton-scattering at the NewSUBARU synchrotron radiation facility. The photoneutron data are used to constrain the $\gamma$-ray strength function on the basis of the Hartree-Fock-Bogolyubov plus quasi-particle random phase approximation using the Gogny D1M interaction. Supplementing the experimentally constrained $\gamma$-ray strength function with the zero-limit E1 and M1 contributions which are unique to the deexcitation mode, we discuss radiative neutron capture cross sections relevant to the s-process nucleosynthesis of barium isotopes in the vicinity of the neutron magic number 82., Comment: arXiv admin note: substantial text overlap with arXiv:1811.00291, arXiv:1804.07654

CITATION: Brits, C. P., et al. 2019. Nuclear level densities and γ-ray strength functions of 180,181,182Ta. Physical Review C, 99(5):054330, doi:10.1103/PhysRevC.99.054330.

Viable theoretical predictions of photon strength functions (PSFs) covering the whole nuclear chart are ofgreat interest for different nuclear applications, including, in particular, nuclear astrophysics. Recently, sucha global PSF model consisting of axially deformed Hartree-Fock-Bogolyubov (HFB) + quasiparticle randomphase approximation (QRPA) calculations with the D1M Gogny interaction and a phenomenological low-energycontribution was proposed. In the present paper, we test this model predictions against previously published datafrom measurements of multistep γ cascades following neutron capture on isolated resonances performed withthe DANCE detector. Such data present a stringent test of the PSFs models, in particular for the properties of theM1 scissors mode and the possible low-energy PSFs enhancement. A detailed comparison is made for spectraobtained from resonances for spherical, quasispherical, and well-deformed nuclei. This comparison indicatesthat the location and strength of the scissors mode is reasonably described by the HFB + QRPA approach.Moreover, a low-energy PSF contribution, not predicted by the HFB + QRPA calculation of the photoabsorptionPSF, should be present in all nuclei. A systematics of this low-energy contribution, assumed in the M1 PSF, isproposed., SCOPUS: ar.j, info:eu-repo/semantics/published

Photoneutron cross sections were measured for $^{203}\mathrm{Tl}$ and $^{205}\mathrm{Tl}$ at energies between the one- and two-neutron thresholds using quasimonochromatic $\ensuremath{\gamma}$-ray beams produced in laser Compton scattering at the NewSUBARU synchrotron radiation facility. Our measurement results in cross sections significantly different from the previously reported bremsstrahlung experiment, leading to rather different giant dipole resonance (GDR) parameters, in particular to lower GDR peak energies and higher peak cross sections. The photoneutron data are used to constrain the $\ensuremath{\gamma}$-ray strength function on the basis of the Hartree-Fock-Bogolyubov plus quasiparticle random-phase approximation using the Gogny D1M interaction. Supplementing the experimentally constrained $\ensuremath{\gamma}$-ray strength function with the zero-limit $E1$ and $M1$ contributions for the de-excitation mode, we estimate the Maxwellian-averaged cross section for the s-process branching-point nucleus $^{204}\mathrm{Tl}$ in the context of the $^{205}\mathrm{Pb}\ensuremath{-}^{205}\mathrm{Tl}$ chronometry.

The success encountered in the systematic studies of the electric and magnetic strength functions for almost all even-even nuclei proves the quality of our HFB+QRPA calculations which use the Gogny interaction within the whole nuclear chart. In this paper, we study the dipole electromagnetic strength distribution in 158-166Dy. The scalar or the vector nature, in the isospin as well as in the spin space, is analysed according to transition density for some of the M1 excitations in 162Dy., SCOPUS: ar.j, info:eu-repo/semantics/published

We present an upgraded version of the SPY model, called SPY2 for version 2 of the scission point yield, toestimate mainly the yields and the kinetic energy distributions of fission fragments: The theoretical frameworkis similar to our previous version, i.e. a statistical scission point model, but this version is based on fullymicroscopic nuclear ingredients describing the fragments properties at the scission point. These include the staticproperties of some 7000 nuclei at 120 axial quadrupole deformations, such as binding energies, proton densities,single-particle level schemes, and states densities, coherently calculated within the constrained Hartree-Fock-Bogoliubov model on the basis of the Skyrme BSk27 interaction. The use of microscopic ingredients has beenextended to the proton density distribution and the nuclear states densities. Considering realistic proton densitiesof fragments allows us to improve the definition of the scission point as well as the prediction of the kineticenergy distribution and to link the kinetic energy to the diffuseness of the fragments’ proton density. Newmicroscopic nuclear states densities improve the general coherence of the model, in particular regarding theinclusion of the odd-even pairing effect. In this updated SPY2 version, the calculation of the fission yieldsand kinetic energy distributions is significantly improved and found to be in relatively good agreement withexperiments, at least qualitatively. A detailed study is performed for three well known fissioning systems, namely,thermal neutron induced fission of 235U and 239Pu and spontaneous fission of 252Cf. A systematic analysis of thefission mode as well as mean fragments deformation and total kinetic energies has been performed for some2000 fissioning nuclei with 78, SCOPUS: ar.j, info:eu-repo/semantics/published

Inelastic (n,n') cross section is a key quantity to accurately simulate reactor cores, and its precision was shown to need significant improvements. To bypass the experimental difficulties to detect neutrons from (n,xn) reaction and to discriminate inelastically scattered neutrons from those following the fission process in case of fissile targets, an indirect but yet powerful method is used: the prompt γ-ray spectroscopy. Along this line, our collaboration has developed the GRAPhEME setup, optimized for actinides, at the GELINA facility to measure partial (n,xn γ) cross sections, from which the total (n,xn) cross section can be inferred. (n,xn γ) experiments with actinides are still particularly challenging, as their structure presents a high level density at low energy, and the competing neutron-induced fission reaction contaminates the γ-energy distribution. New precise measurements of the partial (n,xn γ) cross sections provide a stringent test to theoretical model and offer a way to improve them. This is a path to a better determination of the total inelastic scattering cross sections. In this contribution we discuss modeling aspects of the 238U and 182W (n,n' γ) reactions, also measured with GRAPhEME, using the three codes TALYS, EMPIRE and CoH. We will highlight the needed/expected improvements on reaction modeling and nuclear structure input.

Photoneutron cross sections were measured for Ni58,Ni60,Ni61, and Ni64 at energies between the one-neutron and two-neutron thresholds using quasimonochromatic γ-ray beams produced in laser Compton scattering at the NewSUBARU synchrotron radiation facility. These photoneutron data are used to extract the γ-ray strength function above the neutron threshold, complementing the information obtained by the Oslo method below the threshold. We discuss radiative neutron-capture cross sections and the Maxwellian-averaged cross sections for Ni isotopes including Ni63, a branching point nucleus along the weak s-process path. The cross sections are calculated with the experimentally constrained γ-ray strength functions from the Hartree-Fock-Bogolyubov plus quasiparticle–random-phase approximation based on the Gogny D1M interaction for both E1 and M1 components and supplemented with the M1 upbend.

Nuclear reaction modelling relies on three main theoretical models connected together, namely the optical model, the pre-equilibrium model and the compound nucleus model. Each of these models makes use of various input data, which can either be directly obtained from experiment or from experimentally-based systematics, fine-tuned to reproduce data of interest, or deduced from more fundamental bases. For well measured nuclei, one usually adopts phenomenological approaches consisting in fine-tuning input parameters to fit at best important experimental measurements. However, when dealing with reactions on exotic targets far from the valley of stability, alternatives to risky input data extrapolation have to be considered. Thanks to the high computer power available nowadays, all the input data required to model a nuclear reaction can now be (and have been) microscopically (or semi-microscopically) determined starting from the information provided by a nucleon–nucleon effective interaction. This concerns nuclear masses, optical model potential, total nuclear level densities, photon strength functions, as well as fission paths. Both the quality of these ingredients and the impact of using them instead of the usually adopted phenomenological parameters will be discussed. Perspectives will also be drawn for the coming years on the improvement one can expect with respect to the quality of these ingredients or to the theoretical models using them., SCOPUS: cp.p, info:eu-repo/semantics/published

International audience; Nowadays, reliance on nuclear models to interpolate or extrapolate between experimental data points is very common, for nuclear data evaluation. It is also well known that the knowledge of nuclear reaction mechanisms is at best approximate, and that their modeling relies on many parameters which do not have a precise physical meaning outside of their specific implementations in nuclear model codes: they carry both specific physical information, and effective information that is related to the deficiencies of the model itself. Therefore, to improve the uncertainties associated with evaluated nuclear data, the models themselves must be refined so that their parameters can be rigorously derived from theory. Examples of such a process will be given for a wide sample of models like: detailed theory of compound nucleus decay through multiple nucleon or gamma emission, or refinements to the width fluctuation factor of the Hauser-Feshbach model. All these examples will illustrate the reduction in the effective components of nuclear model parameters, through the reduced dynamics of parameter adjustment needed to account for experimental data. The significant progress, recently achieved for the non-fission channels, also highlights the difficult path ahead to improve our quantitative understanding of fission in a similar way: by relying on microscopic theory.

Inelastic reactions ((n,xn) for x ≥ 1) play a key role in reactor cores as they influence the slowing down of the neutrons. A reactor neutron energy spectrum depends thus on this process which is in strong competition with elastic scattering and fission; a nice example is the case of 238U. Inelastic scattering (x = 1) impacts keff and radial power distribution in the nuclear reactor. For several years, it has been shown that the knowledge of the inelastic cross sections in nuclear databases is not good enough to accurately simulate reactor cores and a strong demand for new measurements has emerged with very tight objectives (only a few percent) for the uncertainties on the cross section. To bypass the well-known experimental difficulty to detect neutrons, the prompt γ-ray spectroscopy method is a powerful but indirect way to obtain inelastic cross sections. Our collaboration has used this method for more than ten years and have produced a lot of (n,n′γ) cross sections for nuclei from 7Li to 238U. In this article, we will first discuss the issues of the prompt γ-ray spectroscopy regarding the control of all the uncertainties involved in the (n,n′γ) cross section estimation. Secondly, we will focus on the role of theoretical modeling which, in certain cases, is crucial to reach the objectives of a few percent uncertainty on the (n,n′) cross sections.

The photoneutron cross sections of Dy162,163 have been measured for the first time in an energy region from the neutron threshold (Sn) up to ≈13MeV. The (γ,n) reaction was induced with quasimonochromatic laser Compton-scattered γ rays, produced at the NewSUBARU laboratory. The corresponding γ-ray strength functions (γSF) have been calculated from the photoneutron cross sections. The data are compared to reanalyzed γSFs of Dy160-164, which are measured below Sn. The excellent agreement with the photoneutron data at Sn confirms the principle of detailed balance. Thus, a complete γSF is established covering in total the energy region of 1≤Eγ≤13 MeV. These mid-shell well-deformed dysprosium isotopes all show scissors resonances with very similar structures. We find that our data predict the same integrated scissors strength as (γ,γ′) data when integrated over the same energy range, which shows that the scissors mode very likely is consistent with the generalized Brink hypothesis. Finally, using the γSFs as input in the reaction code talys, we have deduced radiative neutron-capture cross sections and compared them to direct measurements. We find a very good agreement within the uncertainties, which gives further support to the experimentally determined γSFs., SCOPUS: ar.j, info:eu-repo/semantics/published

International audience; The Gogny D1M potential energy surfaces are used to extract the fission barrier of a large number of nuclei and to study in a systematic way the evolution of the fission barrier height depending on the proton and neutron numbers to deduce possible links with nuclear shell closures and are compared with evaluated nuclear data. The least-action paths are also computed, using Dijkstra's algorithm, and compared to the least-energy paths. Spontaneous fission half-lives are also calculated and compared with experimental data.

The need for nuclear data far from the valley of stability, for applications such as nuclear astrophysics or future nuclear facilities, challenges the robustness as well as the predictive power of present nuclear models. Most of the nuclear data evaluation and prediction are still performed on the basis of phenomenological nuclear models. For the last decades, important progress has been achieved in fundamental nuclear physics, making it now feasible to use more reliable, but also more complex microscopic or semi-microscopic models in the evaluation and prediction of nuclear data for practical applications. Nowadays mean-field models can be tuned at the same level of accuracy as the phenomenological models, renormalized on experimental data if needed, and therefore can replace the phenomenological inputs in the evaluation of nuclear data. The latest achievements to determine nuclear masses within the non-relativistic HFB approach, including the related uncertainties in the model predictions, are discussed. Similarly, recent efforts to determine fission observables within the mean-field approach are described and compared with more traditional existing models., SCOPUS: cp.p, info:eu-repo/semantics/published

The Hauser-Feshbach codes, EMPIRE, TALYS, CCONE, and CoH3 , which are widely utilized in nuclear data evaluations, are compared, with a particular focus on neutron-induced reactions on major actinides. We report the results of Hauser-Feshbach calculations using well-defined input parameters, and discuss the differences among these codes.

Dipole excitations of nuclei are crucial since they play an important role in nuclear reaction modeling in connection with the photoabsorption and the radiative capture processes. We present here results for the gamma-ray strength function obtained in large-scale axially-symmetric deformed quasiparticle (qp) random phase approximations approach using the finite-range Gogny force, with a particular emphasis on the E1 mode. The convergence with respect to the number of harmonic oscillator shells adopted and the cut-off introduced in the 2-quasiparticle excitation energy space is analyzed. The microscopic nature of our self-consistent Hartree-Fock-Bogoliubov plus QRPA (HFB+QRPA) calculation has unfortunately to be broken, some phenomenological corrections being needed to take into account effects beyond the standard 2-qp QRPA excitations and the coupling between the single-particle and low-lying collective phonon degrees of freedom. The corresponding phenomenological parameters are adjusted on experimental photoabsorption data. In such a procedure, a rather satisfactory description of experimental data is obtained. To study the sensitivity of these phenomenological corrections on the extrapolation, both at low energies and towards exotic neutron-rich nuclei, three different prescriptions are considered. They are shown to lead to rather similar predictions of the E1 strength at low energies as well as for exotic neutron-rich nuclei. The Gogny-HFB+QRPA strength is finally applied to the calculation of radiative neutron capture cross sections and the predictions compared with those obtained with more traditional Lorentzian-type approaches., SCOPUS: cp.p, info:eu-repo/semantics/published

The experimental setup GRAPhEME (GeRmanium array for Actinides PrEcise MEasurements) has been used at GELINA (EC-JRC, Geel, Belgium) to perform (n,xn γ) cross sections measurements. GRAPhEME has been especially designed to take into account the specific difficulties generated by the use of actinides samples. This work takes place in the context of new nuclear data measurements for nuclear reactor applications. Considering the very tight accuracy requested for new experimental data, special care has been paid to quantify as accurately as possible all the uncertainties from the instruments and the analysis procedure. From the precise (n,xn γ) cross sections produced with GRAPhEME, the use of model calculations is required to obtain (n,xn) cross sections. Beyond the measurements, extensive work on theoretical models is necessary to achieve a better evaluation of the (n,xn) processes. In this paper, we will discuss the final step of the 238 U data analysis and present some recent results obtained on 232 Th compared to TALYS modellings. A new measurement campaign on 233 U has started recently, a first assessment of the recorded data will be presented.

Recent increases in computing power have allowed for much progress to be made in the field of nuclear data. The advances listed below are each significant, but together bring the potential to completely change our perspective on the nuclear data evaluation process. The use of modern nuclear modeling codes like TALYS and the Monte Carlo sampling of its model parameter space, together with a code system developed at NRG Petten, which automates the production of ENDF-6 formatted files, their processing, and their use in nuclear reactor calculations, constitutes the Total Monte Carlo approach, which directly links physical model parameters with calculated integral observables like keff. Together with the Backward-Forward Monte Carlo method for weighting samples according their statistical likelihood, the Total Monte Carlo can be applied to complete isotopic chains in a consistent way, to simultaneously evaluate nuclear data and the associated uncertainties in the continuum region. Another improvement is found in the uses of microscopic models for nuclear reaction calculations. For example, making use of QRPA excited states calculated with the Gogny interaction to solve the long standing question of the origin of the ad hoc "pseudo-states" that are introduced in evaluated nuclear data files to account for the Livermore pulsed sphere experiments. A third advance consists of the recent optimization of the Gogny D1M effective nuclear interaction, including constraints from experimental nuclear masses at the "beyond the mean field" level. All these advances are only made possible by the availability of vast resources of computing power, and even greater resources will allow connecting them, going continuously from the parameters of the nuclear interaction to reactor calculations. However, such scheme will surely only be usable for applications if a few fine-tuning "knobs" are introduced in it. The values of these adjusted parameters will have to be calibrated versus differential and integral experimental constraints. © 2014., SCOPUS: ar.j, info:eu-repo/semantics/published

The structure of neutron-rich 96,98Sr nuclei was investigated by low-energy safe Coulomb excitation of radioactive beams at the REX-ISOLDE facility, CERN, with the MINIBALL spectrometer. A rich set of transitional and diagonal E2 matrix elements, including those for non-yrast structures, has been extracted from the differential Coulomb-excitation cross sections. The results support the scenario of a shape transition at N = 60, giving rise to the coexistence of a highly deformed prolate and a spherical configuration in 98Sr, and are compared to predictions from several theoretical calculations. The experimental data suggest a significant contribution of the triaxal degree of freedom in the ground state of both isotopes. In addition, experimental information on low-lying states in 98Rb has been obtained.

Valuable theoretical predictions of nuclear dipole excitations in the whole chart are of great interest for different nuclear applications, including in particular nuclear astrophysics. Here we extend our large-scale calculations of the $E1 \ensuremath{\gamma}$-ray strength function, obtained in the framework of the axially- symmetric-deformed quasiparticle random phase approximation (QRPA) based on the finite-range D1M Gogny force, to the calculation of the $M1$ strength function. We compare our QRPA prediction of the $M1$ strength with available experimental data and show that a relatively good agreement is obtained provided the strength is shifted globally by about 2 MeV and increased by an empirical factor of 2. Predictions of the $M1$ strength function for spherical and deformed nuclei within the valley of $\ensuremath{\beta}$ stability as well as in the neutron-rich region are discussed. Its impact on the radiative neutron capture cross section is also analyzed.

International audience; An optimized broadband source emitting from 1064 to 1600 nm was specially designed for coherent anti-Stokes Raman scattering spectroscopy. This source is based on the use of a ytterbium-doped photonic crystal fiber with a large core in which a supercontinuum is generated from a signal wave at 1064 nm regenerated by ytterbium ions pumping. A particularly flat spectrum with high spectral power density and perfectly synchronized spectral components is obtained.

Valuable theoretical predictions of nuclear dipole excitations in the whole chart are of great interest for different nuclear applications, including in particular nuclear astrophysics. Here we present large-scale calculations of the $E1\phantom{\rule{4pt}{0ex}}\ensuremath{\gamma}$-ray strength function obtained in the framework of the axially symmetric deformed quasiparticle random-phase approximation based on the finite-range Gogny force. This approach is applied to even-even nuclei, the strength function for odd nuclei being derived by interpolation. The convergence with respect to the adopted number of harmonic oscillator shells and the cutoff energy introduced in the 2-quasiparticle $(2\ensuremath{-}qp)$ excitation space is analyzed. The calculations performed with two different Gogny interactions, namely D1S and D1M, are compared. A systematic energy shift of the $E1$ strength is found for D1M relative to D1S, leading to a lower energy centroid and a smaller energy-weighted sum rule for D1M. When comparing with experimental photoabsorption data, the Gogny-QRPA predictions are found to overestimate the giant dipole energy by typically $\ensuremath{\sim}2$ MeV. Despite the microscopic nature of our self-consistent Hartree-Fock-Bogoliubov plus QRPA calculation, some phenomenological corrections need to be included to take into account the effects beyond the standard $2\ensuremath{-}qp$ QRPA excitations and the coupling between the single-particle and low-lying collective phonon degrees of freedom. For this purpose, three prescriptions of folding procedure are considered and adjusted to reproduce experimental photoabsorption data at best. All of them are shown to lead to somewhat similar predictions of the $E1$ strength, both at low energies and for exotic neutron-rich nuclei. Predictions of $\ensuremath{\gamma}$-ray strength functions and Maxwellian-averaged neutron capture rates for the whole Sn isotopic chain are also discussed and compared with previous theoretical calculations.

The increasing need for cross sections far from the valley of stability poses a challenge for nuclear reaction models. So far, predictions of cross sections have relied on more or less phenomenological approaches, depending on parameters adjusted to available experimental data or deduced from systematic expressions. While such predictions are expected to be reliable for nuclei not too far from the experimentally known regions, it is clearly preferable to use more fundamental approaches, based on sound physical principles, when dealing with very exotic nuclei. Thanks to the high computer power available today, all the ingredients required to model a nuclear reaction can now be (and have been) microscopically (or semi-microscopically) determined starting from the information provided by a nucleon-nucleon effective interaction. This concerns nuclear masses, optical model potential, nuclear level densities, photon strength functions, as well as fission barriers. All these nuclear model ingredients, traditionally given by phenomenological expressions, now have a microscopic counterpart implemented in the TALYS nuclear reaction code. We are thus now able to perform fully microscopic cross section calculations. The quality of these ingredients and the impact of using them instead of the usually adopted phenomenological parameters will be discussed. Perspectives for the coming years will be drawn on the improvements one can expect., info:eu-repo/semantics/published

Neutron-rich {96,98}Sr isotopes have been investigated by safe Coulomb excitation of radioactive beams at the REX-ISOLDE facility. Reduced transition probabilities and spectroscopic quadrupole moments have been extracted from the differential Coulomb excitation cross sections. These results allow, for the first time, the drawing of definite conclusions about the shape coexistence of highly deformed prolate and spherical configurations. In particular, a very small mixing between the coexisting states is observed, contrary to other mass regions where strong mixing is present. Experimental results have been compared to beyond-mean-field calculations using the Gogny D1S interaction in a five-dimensional collective Hamiltonian formalism, which reproduce the shape change at N=60.

About half of the nuclei heavier than iron observed in nature are produced by the so-called rapid neutron capture process, or r-process, of nucleosynthesis. The identification of the astrophysics site and the specific conditions in which the r-process takes place remains, however, one of the still-unsolved mysteries of modern astrophysics. Another underlying difficulty associated with our understanding of the r-process concerns the uncertainties in the predictions of nuclear properties for the few thousands exotic neutron-rich nuclei involved, for which essentially no experimental data exist.The present paper emphasizes some important future challenges faced by nuclear physics in this problem, particularly in the determination of the nuclear structure properties of exotic neutron-rich nuclei as well as their radiative neutron capture rates and their fission probabilities. These quantities are particularly relevant to determine the composition of the matter resulting from the r-process. Both the astrophysics and the nuclear physics difficulties are critically reviewed with special attention paid to the r-process taking place during the decompression of neutron star matter following the merging of two neutron stars., SCOPUS: cp.j, info:eu-repo/semantics/published, Nuclear Physics in Astrophysics VI (NPA6)19–24 May 2013, Lisbon, Portugal

International audience; We present the Gogny-Hartree-Fock-Bogoliubov model which reproduces nuclear masses with an accuracy comparable with the best mass formulas. In contrast to the Skyrme-HFB nuclear-mass models, an explicit and self-consistent account of all the quadrupole correlation energies is included within the 5D collective Hamiltonian approach. The final rms deviation with respect to the 2353 measured masses is 789keV in the 2012 atomic mass evaluation. In addition, the D1M Gogny force is shown to predict nuclear and neutron matter properties in agreement with microscopic calculations based on realistic two- and three-body forces. The D1M properties and its predictions of various observables are compared with those of D1S and D1N.

International audience; Extensive nuclear structure studies have been performed for decades using effective interactions as sole input. They have shown a remarkable ability to describe rather accurately many types of nuclear properties. In the early 2000s, a major effort has been engaged to produce nuclear reaction input data out of the Gogny interaction, in order to challenge its quality also with respect to nuclear reaction observables. The status of this project, well advanced today thanks to the use of modern computers as well as modern nuclear reaction codes, is reviewed and future developments are discussed.

International audience; A model to calculate particle-induced reaction cross sections with statistical Hauser-Feshbach theory including direct reactions is given. The energy average of the scattering matrix from the coupled-channels optical model is diagonalized by the transformation proposed by Engelbrecht and Weidenmüller [C. A. Engelbrecht and H. A. Weidenmüller, Phys. Rev. C 8, 859 (1973)PRVCAN0556-281310.1103/PhysRevC.8.859]. The ensemble average of S-matrix elements in the diagonalized channel space is approximated by a model of Moldauer [P. A. Moldauer, Phys. Rev. C 12, 744 (1975)PRVCAN0556-281310.1103/PhysRevC.12.744] using the newly parametrized channel degree-of-freedom νa to better describe the Gaussian orthogonal ensemble (GOE) reference calculations. The Moldauer approximation is confirmed by a Monte Carlo study using a randomly generated S matrix, as well as the GOE threefold integration formula. The method proposed is applied to the U238(n,n′) cross-section calculation in the fast-energy range, showing an enhancement in the inelastic scattering cross sections.

A microscopic nuclear reaction model is applied to neutron elastic and direct inelastic scatterings, and pre-equilibrium reaction. The JLM folding model is used with nuclear structure information calculated within the quasi-particle random phase approximation implemented with the Gogny D1S interaction. The folding model for direct inelastic scattering is extended to include rearrangement corrections stemming from both isoscalar and isovector density variations occurring during a transition. The quality of the predicted (n,n), (n, $n^{\prime}$ ), (n,xn) and ( $n,n^{\prime}\gamma$ cross sections, as well as the generality of the present microscopic approach, shows that it is a powerful tool that can help improving nuclear reactions data quality. Short- and long-term perspectives are drawn to extend the present approach to more systems, to include missing reactions mechanisms, and to consistently treat both structure and reaction problems.

The combinatorial model of nuclear level densities has now reached a level of accuracy comparable to that of the best global analytical expressions without suffering from the limits imposed by the statistical hypothesis on which the latter expressions rely. In particular, it provides naturally, non Gaussian spin distribution as well as non equipartition of parities which are known to have a significant impact on cross section predictions at low energies [1, 2]. Our first global model developed in Ref. 1 su ered from deficiencies, in particular in the way the collective effects -both vibrational and rotational - were treated. We have recently improved this treatment using simultaneously the single particle levels and collective properties predicted by a newly derived Gogny interaction [3], therefore enabling a microscopic description of energy-dependent shell, pairing and deformation e effects. In addition, for deformed nuclei, the transition to sphericity is coherently taken into account on the basis of a temperature-dependent Hartree-Fock calculation which provides at each temperature the structure properties needed to build the level densities. This new method is described and shown to give promising preliminary results with respect to available experimental data.

Mean-field calculations can nowadays provide all the nuclear ingredients required to describe the fission path from the equilibrium deformation up to the nuclear scission point. The information obtained from microscopic mean-field models has been included in reaction codes to improve the predictions of neutron-induced fission cross section. The nuclear inputs concern not only the details of the energy surface along the fission path, but also the coherent estimate of the nuclear level density derived within the combinatorial approach on the basis of the same single-particle properties, in particular at the fission saddle points. The predictive power of such a microscopic approach is tested. It is also shown that the various inputs can be tuned to reproduce at best experimental data in one unique coherent framework, so that it is now possible to make reliable and accurate fission cross-section calculations on the basis of microscopic models, but also to use such approaches to estimate the corresponding modeling uncertainties for nuclei, energy ranges or reaction channels for which no data exist.

Yield-weighted average cross sections of neutron radiative capture, (n,2n), and (n,3n) reactions over prompt fission products (FPs) from 235U and 239Pu are calculated. The prompt fission production yields are taken from the ENDF/B-VII.0 library. The FPs for each fissile material exist over a range of approximately 1000 neutron-rich nuclides. Several nuclear reaction codes are utilized for calculating the cross sections on each individual fission product—EMPIRE-2.19, TALYS-1.0, GNASH, and CoH. The influence of the FP isomers on the average cross sections is examined with TALYS. We investigate the dependence of the average cross sections on the number of FPs taken for averaging. It is shown that the average capture cross section is much more sensitive to the number of FPs included, compared with the (n,2n) and (n,3n) reactions. An intercomparison of the calculated cross sections with the different reaction codes is carried out. In the capture reaction, EMPIRE predicted lower cross section than TALYS and CoH...

Valuable theoretical predictions of nuclear dipole excitations in the whole chart are of great interest for different nuclear applications, including in particular nuclear astrophysics. Here we extend our large-scale calculations of the E1 and M1 absorption γ-ray strength function obtained in the framework of the axially-symmetric deformed quasiparticle random phase approximation (QRPA) based on the finite-range D1M Gogny force to the determination of the de-excitation strength function. To do so, shell-model calculations of the de-excitation dipole strength function as well as experimental data are considered to provide insight in the low-energy limit and to complement the QRPA estimate phenomenologically. We compare our final prediction of the E1 and M1 strengths with available experimental data at low energies and show that a relatively good agreement can be obtained. Its impact on the average radiative width as well as radiative neutron capture cross section is discussed., SCOPUS: cp.p, info:eu-repo/semantics/published

We describe the physics and data included in the Reference Input Parameter Library, which is devoted to input parameters needed in calculations of nuclear reactions and nuclear data evaluations. Advanced modelling codes require substantial numerical input, therefore the International Atomic Energy Agency (IAEA) has worked extensively since 1993 on a library of validated nuclear-model input parameters, referred to as the Reference Input Parameter Library (RIPL). A final RIPL coordinated research project (RIPL-3) was brought to a successful conclusion in December 2008, after 15 years of challenging work carried out through three consecutive IAEA projects. The RIPL-3 library was released in January 2009, and is available on the Web through (http://www-nds.iaea.org/RIPL-3/). This work and the resulting database are extremely important to theoreticians involved in the development and use of nuclear reaction modelling (ALICE, EMPIRE, GNASH, UNF, TALYS) both for theoretical research and nuclear data evaluations. The numerical data and computer codes included in RIPL-3 are arranged in seven segments: MASSES contains ground-state properties of nuclei for about 9000 nuclei, including three theoretical predictions of masses and the evaluated experimental masses of Audi et al. (2003). DISCRETE LEVELS contains 117 datasets (one for each element) with all known level schemes, electromagnetic andmore » {gamma}-ray decay probabilities available from ENSDF in October 2007. NEUTRON RESONANCES contains average resonance parameters prepared on the basis of the evaluations performed by Ignatyuk and Mughabghab. OPTICAL MODEL contains 495 sets of phenomenological optical model parameters defined in a wide energy range. When there are insufficient experimental data, the evaluator has to resort to either global parameterizations or microscopic approaches. Radial density distributions to be used as input for microscopic calculations are stored in the MASSES segment. LEVEL DENSITIES contains phenomenological parameterizations based on the modified Fermi gas and superfluid models and microscopic calculations which are based on a realistic microscopic single-particle level scheme. Partial level densities formulae are also recommended. All tabulated total level densities are consistent with both the recommended average neutron resonance parameters and discrete levels. GAMMA contains parameters that quantify giant resonances, experimental gamma-ray strength functions and methods for calculating gamma emission in statistical model codes. The experimental GDR parameters are represented by Lorentzian fits to the photo-absorption cross sections for 102 nuclides ranging from {sup 51}V to {sup 239}Pu. FISSION includes global prescriptions for fission barriers and nuclear level densities at fission saddle points based on microscopic HFB calculations constrained by experimental fission cross sections.« less

A new parameterization of the effective nucleon–nucleon Gogny interaction is proposed. It reproduces the neutron matter equation of state much better than the commonly used D1S Gogny interaction and furthermore reduces the binding energies' drift for the major part of the isotopic chains. Other important nuclear properties related both to nuclear matter and finite nuclei are studied and shown to be of similar quality as with D1S.

Four different level density models, three phenomenological and one microscopic, are consistently parameterized using the same set of experimental observables. For each of the phenomenological models, the Constant Temperature Model, the Back-shifted Fermi gas Model and the Generalized Superfluid Model, a version without and with explicit collective enhancement is considered. Moreover, a recently published microscopic combinatorial model is compared with the phenomenological approaches and with the same set of experimental data. For each nuclide for which sufficient experimental data exists, a local level density parameterization is constructed for each model. Next, these local models have helped to construct global level density prescriptions, to be used for cases for which no experimental data exists. Altogether, this yields a collection of level density formulae and parameters that can be used with confidence in nuclear model calculations. To demonstrate this, a large-scale validation with experimental discrete level schemes and experimental cross sections and neutron emission spectra for various different reaction channels has been performed.

Yttrium plays an important role as a radiochemical dosimetry detector for determining high energy 14 MeV neutron fluences, through measurement of (n,2n) activation products. The total (n,2n) cross section is known rather well from extensive activation measurements on the stable 89Y isotope, and from a previous activation measurement on the unstable 88Y ground state. However, until now the branching ratios to the ground state and excited isomers in 88Y via the 89Y (n,2n) reaction were not well known, and furthermore, uncertainty estimates were not available for these cross sections and branching ratios. This paper describes how gamma-ray transitions between states in (n,2n) and (n,n') reactions measured using the GEANIE detector at Los Alamos' LANSCE facility, together with theory predictions using the GNASH code, enable us to determine these quantities for the ENDF/B-VII evaluation. A previous measurement by Dietrich, at Livermore, provided important complementary information to the GEANIE analysis. We describe an uncertainty quantification analysis that uses the GNASH-KALMAN approach to evaluate cross sections for the 89Y (n,2n) population of the 88Y ground state and two meta-stable isomers (m1 and m2), along with their uncertainties. Our new results agree with Arthur's historic Los Alamos evaluated cross sections within a few percent below 15 MeV (with larger differences above 15 MeV). The (n,2n) cross sections to the 88Y ground state and m1, m2 isomers impact the average 88Y(n,2n)87Y cross section at leading-order; we determine this 14.1 MeV average cross section 88Y(n,2n)87Y = 1107 mb (± 4%), which agrees with the value obtained from Arthur's evaluation to 0.7%. An alternative method to predict cross sections, uncertainties, and covariance data, is described that uses the European TALYS reaction modeling code and a Backward-Forward Monte-Carlo uncertainty quantification technique. This approach uses a microscopic optical model, together with Hauser-Feshbach and preequilibrium reaction mechanisms, and the underlying model parameters and their uncertainties and correlations are determined through a Monte-Carlo filtering method based on comparisons with measured cross section data. We compare the results obtained using this approach with the GNASH-KALMAN method. The evaluated cross sections are rather similar in the two approaches. We show how the uncertainty information, as embodied in the resulting covariance matrices, is also qualitatively similar in both approaches.

Large-scale axial mean-field calculations from proton to neutron drip lines have been performed within the Hartree-Fock-Bogoliubov method based on the D1S Gogny force. Nearly 7000 nuclides have been studied under the axial symmetric hypothesis and various properties are displayed on an Internet web site for every individual nucleus. Some global properties are presented such as the positions of the drip lines, the nuclide ground-state deformations and binding energies as well as regions where possible super- or hyper-deformation might be encountered.

The development of high performance computing facilities makes possible a massive production of nuclear data in a full microscopic framework. Taking advantage of the individual potential calculations of more than 7000 nuclei, a new statistical scission-point model, called SPY, has been developed. It gives access to the absolute available energy at the scission point, which allows the use of a parameter-free microcanonical statistical description to calculate the distributions and the mean values of all fission observables. SPY uses the richness of microscopy in a rather simple theoretical framework, without any parameter except the scission-point definition, to draw clear answers based on perfect knowledge of the ingredients involved in the model, with very limited computing cost.