Search

Black-hole (BH) accretion disks formed in compact-object mergers or collapsars may be major sites of the rapid-neutron-capture (r-)process, but the conditions determining the electron fraction (Y_e) remain uncertain given the complexity of neutrino transfer and angular-momentum transport. After discussing relevant weak-interaction regimes, we study the role of neutrino absorption for shaping Y_e using an extensive set of simulations performed with two-moment neutrino transport and again without neutrino absorption. We vary the torus mass, BH mass and spin, and examine the impact of rest-mass and weak-magnetism corrections in the neutrino rates. We also test the dependence on the angular-momentum transport treatment by comparing axisymmetric models using the standard alpha-viscosity with viscous models assuming constant viscous length scales (l_t) and three-dimensional magnetohydrodynamic (MHD) simulations. Finally, we discuss the nucleosynthesis yields and basic kilonova properties. We find that absorption pushes Y_e towards ~0.5 outside the torus, while inside increasing the equilibrium value Y_e^eq by ~0.05-0.2. Correspondingly, a substantial ejecta fraction is pushed above Y_e=0.25, leading to a reduced lanthanide fraction and a brighter, earlier, and bluer kilonova than without absorption. More compact tori with higher neutrino optical depth, tau, tend to have lower Y_e^eq up to tau~1-10, above which absorption becomes strong enough to reverse this trend. Disk ejecta are less (more) neutron-rich when employing an l_t=const. viscosity (MHD treatment). The solar-like abundance pattern found for our MHD model marginally supports collapsar disks as major r-process sites, although a strong r-process may be limited to phases of high mass-infall rates, Mdot>~ 2 x 10^(-2) Msun/s., 37 pages, 22 figures, 5 tables, accepted to MNRAS, minor changes compared to previous version

We study the enrichment of the interstellar medium with rapid neutron capture (r-process) elements produced in binary neutron star (BNS) mergers. We use a semi-analytic model to describe galactic evolution, with merger rates and time delay distributions of BNS mergers consistent with the latest population synthesis models. In order to study the dispersion of the relative abundances of r-process elements and iron, we applied a turbulent mixing scheme, where the freshly synthesized elements are gradually dispersed in the interstellar medium. We show that within our model the abundances observed in Milky-Way stars, in particular the scatter at low metallicities, can be entirely explained by BNS mergers. Our results suggest that binary neutron star mergers could be the dominant source of r-process elements in the Galaxy., Comment: 16 pages, 19 figures. Modified to match the version accepted by MNRAS (some changes to main results and conclusions, new section added)

Photo-induced reaction cross section data are of importance for a variety of current or emerging applications, such as radiation shielding design and radiation transport analyses, calculations of absorbed dose in the human body during radiotherapy, physics and technology of fission reactors (influence of photo-reactions on neutron balance) and fusion reactors (plasma diagnostics and shielding), activation analyses, safeguards and inspection technologies, nuclear waste transmutation, medical isotope production and astrophysical applications. To address these data needs the IAEA Photonuclear Data library was produced in 1999, containing evaluated photo-induced cross sections and neutron spectra for 164 nuclides which were deemed relevant for the applications. Since the release of the IAEA Photonuclear Data Library however, new experimental data as well as new methods to assess the reliability of experimental cross sections have become available. Theoretical models and input parameters used to evaluate photo-induced reactions have improved significantly over the years. In addition, new measurements of partial photoneutron cross sections using mono-energetic photon beams and advanced neutron detection systems have been performed allowing for the validation of the evaluations and assessments of the experimental data. Furthermore, technological advances have led to the construction of new and more powerful gamma-beam facilities, therefore new data needs are emerging. We report our coordinated efforts to address these data needs and present the results of the new up-to-date evaluations included in the new updated IAEA Photonuclear Data Library consisting of 219 nuclides. The new library includes 188 new evaluations produced by the CRP evaluators, and one evaluation taken from the JENDL/PD-2016 library, while 20 evaluations were retained from the previous 1999 IAEA Photonuclear Data Library. In most of the cases, the photon energy goes up to 200 MeV. A total of 55 nuclides are new in this library reflecting the progress in measurements but also the developing data needs. In this paper we discuss the new assessment method and make recommendations to the user community in cases where the experimental data are discrepant and the assessments disagree. In addition, in the absence of experimental data, we present model predictions for photo-induced reaction cross section on nuclides of potential interest to medical radioisotope production.

We present a coherent study of the impact of neutrino interactions on the r-process element nucleosynthesis and the heating rate produced by the radioactive elements synthesised in the dynamical ejecta of neutron star-neutron star (NS-NS) mergers. We have studied the material ejected from four NS-NS merger systems based on hydrodynamical simulations which handle neutrino effects in an elaborate way by including neutrino equilibration with matter in optically thick regions and re-absorption in optically thin regions. We find that the neutron richness of the dynamical ejecta is significantly affected by the neutrinos emitted by the post-merger remnant, in particular when compared to a case neglecting all neutrino interactions. Our nucleosynthesis results show that a solar-like distribution of r- process elements with mass numbers $A \gtrsim 90$ is produced, including a significant enrichment in Sr and a reduced production of actinides compared to simulations without inclusion of the nucleonic weak processes. The composition of the dynamically ejected matter as well as the corresponding rate of radioactive decay heating are found to be rather independent of the system mass asymmetry and the adopted equation of state. This approximate degeneracy in abundance pattern and heating rates can be favourable for extracting the ejecta properties from kilonova observations, at least if the dynamical component dominates the overall ejecta. Part II of this work will study the light curve produced by the dynamical ejecta of our four NS merger models., 18 pages, 21 figures, 2 Tables, accepted by MNRAS 2021-11-19

In this work, covariance matrices coming from model variations, in contrast to the usual parameter variations, are presented. The considered phenomenological and microscopic models are included in the code TALYS, and concern level densities, gamma strength functions, optical potentials and masses. A total of 288 model sets for each isotope is used to estimate both uncertainties and correlations from systematical origin. The calculated quantities are of interest for astrophysical applications, such as capture cross sections, and reaction rates. The isotopes (3 ≤ Z ≤ 100) are from the proton to neutron drip lines, covering about 8800 cases, and are included in the TENDL-2021 library.

Valuable theoretical predictions of nuclear dipole excitations in the whole nuclear chart are of great interest for different applications, including in particular nuclear astrophysics. We present here the systematic study of the electric-dipole ( E 1 ) photon strength functions combining the microscopic Hartree-Fock-Bogoliubov plus quasiparticle random-phase approximation (HFB + QRPA) model and the parametrizations constrained by the available experimental giant dipole resonance (GDR) data. For about 10 000 nuclei with 8 ≤ Z ≤ 124 lying between the proton and the neutron drip-lines on nuclear chart, the particle-hole (ph) strength distributions are computed using the HFB + QRPA model under the assumption of spherical symmetry and making use of the BSk27 Skyrme effective interaction derived from the most accurate HFB mass model (HFB-27) so far achieved. Large-scale calculations of the BSk27 + QRPA E 1 photon strength functions are performed in the framework of a specific folding procedure describing the damping of nuclear collective motion empirically. In particular, three phenomenological improvements are considered in this folding procedure. First, two interference factors are introduced and adjusted to reproduce at best the available experimental GDR data. Second, an empirical expression accounting for the deformation effect is applied to describe the peak splitting of the strength function. Third, the width of the strength function is corrected by a temperature-dependent term, which effectively increases the deexcitation photon strength function at low energy. The theoretical E 1 photon strength functions as well as the extracted GDR peaks and widths are comprehensively compared with available experimental data. A relatively good agreement with data indicates the reliability of the present calculations. Eventually, the astrophysical rates of ( n , γ ) reactions for all the 10 000 nuclei with 8 ≤ Z ≤ 124 lying between the proton and the neutron drip lines are estimated using the present E 1 photon strength functions. The resulting reaction rates are compared with the previous BSk7 + QRPA results as well as the Gogny-HFB + QRPA predictions based on the D1M interaction.

International audience; While the ground state configuration is classically determined by the variational principle minimizing the binding energy of the system, we propose here a different procedure to identify the configuration of the ground state in odd-A nuclei. This procedure is based on the Hartree-Fock-Bogolyubov (HFB) framework with a self-consistent blocking of the unpaired nucleon and identifies the ground state as the blocked quasiparticle configuration compatible with the observed spin and parity and, most importantly, the measured magnetic moment. The magnetic moments are calculated within the HFB framework for all odd Hg isotopes for which experimental data is available. To validate the method, a systematic comparison between the predicted and measured electric quadrupole moments and isotopic shifts is performed. For even-even isotopes, we show that the ground state deformation, and more particularly the competition between the prolate and oblate shapes, can hardly be determined through a comparison of the QRPA β-decay half-life with experiment, though this approach also calls for an observable similar to the one used for odd-A isotopes, namely the spin-flip component of the isovector part of the magnetic moment operator. For even isotopes with shape coexistence, no adequate constraint could be identified, except though the charge radius. Assuming light even-even Hg isotopes to have an oblate shape, the resulting charge radii staggering observed in the Hg chain by laser spectroscopy can through this identification procedure be reproduced.

Recent measurements of the nuclear level densities and γ-ray strength functions below the neutron thresholds in 180,181,182Ta are used as input in the nuclear reaction code TALYS. These experimental average quantities are utilized in the calculations of the 179,180,181Ta radiative neutron capture cross sections. From the latter, astrophysical Maxwellian-averaged (n,γ) cross sections (MACS) and reaction rates are extracted, which in turn are used in large astrophysical network calculations to probe the production mechanism of 180 Ta. These calculations are performed for two scenarios, the s-process production of 180,181Ta in Asymptotic Giant Branch (AGB) stars and the p-process nucleosynthesis of 180Tam in Type-II supernovae. Based on the results from this work, the s-process in stellar evolution is considered negligible in the production of 180Tam whereas 181Ta is partially produced by AGB stars. The new measurements strongly constrain the production and destruction rates of 180Tam at p-process temperatures and confirm significant production of nature’s rarest stable isotope 180Tam by the p-process., SCOPUS: ar.j, info:eu-repo/semantics/published

S stars are late-type giants that are transition objects between M-type stars and carbon stars on the asymptotic giant branch (AGB). They are classified into two types: intrinsic or extrinsic, based on the presence or absence of technetium (Tc). The Tc-rich or intrinsic S stars are thermally-pulsing (TP-)AGB stars internally producing s-process elements (including Tc) which are brought to their surface via the third dredge-up (TDU). Tc-poor or extrinsic S stars gained their s-process overabundances via accretion of s-process-rich material from an AGB companion which has since turned into a dim white dwarf. Our goal is to investigate the evolutionary status of Tc-rich S stars by locating them in a Hertzsprung-Russell (HR) diagram using the results of Gaia early Data Release 3 (EDR3). We combine the current sample of 13 Tc-rich stars with our previous studies of 10 Tc-rich stars to determine the observational onset of the TDU in the metallicity range [-0.7; 0]. We also compare our abundance determinations with dedicated AGB nucleosynthesis predictions. The stellar parameters are derived using an iterative tool which combines HERMES high-resolution spectra, accurate Gaia EDR3 parallaxes, stellar evolution models and tailored MARCS model atmospheres for S-type stars. Using these stellar parameters we determine the heavy-element abundances by line synthesis. In the HR diagram, the intrinsic S stars are located at higher luminosities than the predicted onset of the TDU. These findings are consistent with Tc-rich S stars being genuinely TP-AGB stars. The comparison of the derived s-process abundance profiles of our intrinsic S stars with the nucleosynthesis predictions provide an overall good agreement. Stars with highest [s/Fe] tend to have the highest C/O ratios., 22 pages, 10 figures, accepted for publication in Section 7. Stellar structure and evolution of Astronomy and Astrophysics (A&A)

A new large sample of 895 s-process-rich candidates out of 454180 giant stars surveyed by LAMOST at low spectral resolution (R ~ 1800) has been reported by Norfolk et al. (2019; hereafter N19). We aim at confirming the s-process enrichment at the higher resolution (R ~ 86000) offered by the HERMES-Mercator spectrograph, for the 15 brightest targets of the previous study sample which consists in 13 Sr-only stars and two Ba-only stars. Abundances were derived for elements Li, C, N, O, Na, Mg, Fe, Rb, Sr, Y, Zr, Nb, Ba, La, and Ce. Binarity has been tested by comparing the Gaia DR2 radial velocity with the HERMES velocity obtained 1600 - 1800 days later. Among the 15 programme stars, four show no s-process overabundances ([X/Fe] < 0.2 dex), eight show mild s-process overabundances (at least three heavy elements with 0.2 < [X/Fe] < 0.8), and three have strong overabundances (at least three heavy elements with [X/Fe] > 0.8). Among the 13 stars classified as Sr-only by the previous investigation, four have no s-process overabundances, eight are mild barium stars, and one is a strong barium star. The two Ba-only stars turn out to be both strong barium stars and are actually dwarf barium stars. They also show clear evidence for being binaries. Among the no-s stars, there are two binaries out of four, whereas only one out of the eight mild barium stars show a clear signature of radial-velocity variations. Blending effects and saturated lines have to be considered very carefully when using machine-learning techniques, especially on low-resolution spectra. Among the Sr-only stars from the previous study sample, one may expect about 60% (8/13) of them to be true mild barium stars and about 8% to be strong barium stars, and this fraction is likely close to 100% for the previous study Ba-only stars (2/2)., Accepted for publication in A&A, 15 pages, 12 figures

Results from observations report a growing number of metal-poor stars showing an abundance pattern midway between the s- and r-processes. These so-called r/s-stars raise the need for an intermediate neutron capture process (i-process), which is thought to result from the ingestion of protons in a convective helium-burning region, but whose astrophysical site is still largely debated. We investigate whether an i-process during the asymptotic giant branch (AGB) phase of low-metallicity low-mass stars can develop and whether it can explain the abundances of observed r/s-stars. At the beginning of the AGB phase, during the third thermal pulse, the helium driven convection zone is able to penetrate the hydrogen-rich layers. The subsequent proton ingestion leads to a strong neutron burst with neutron densities of $\approx 4.3 \times 10^{14}$ cm$^{-3}$ at the origin of the synthesis of i-process elements. The nuclear energy released by proton burning in the helium-burning convective shell strongly affects the internal structure: the thermal pulse splits and after approximately ten years the upper part of the convection zone merges with the convective envelope. The surface carbon abundance is enhanced by more than 3 dex. This leads to an increase in the opacity, which triggers a strong mass loss and prevents any further thermal pulse. We show that specific isotopic ratios of Ba, Nd, Sm, and Eu can represent good tracers of i-process nucleosynthesis. Finally, an extended comparison with 14 selected r/s-stars show that the observed composition patterns can be well reproduced by our i-process AGB model., Comment: Published in A&A. This version of the preprint has been corrected (especially Table 2 and Section 6.5) with the modifications appearing in the A&A corrigendum (which is included at the end of the paper)

We present the latest development of measuring (γ, n) cross sections and giant dipole resonance (GDR) cross sections in the IAEA photonuclear data project. Photoneutron cross sections were measured for 21 isotopes below 2n threshold to construct the γ-ray strength function (γSF) with the γSF method; (γ, n) cross sections are used as experimental constraints on the model E1 and M1 γSFs from the Hartree–Fock–Bogolyubov plus quasi-particle random phase approximation based on the Gogny D1M interaction supplemented with the M1 upbend. GDR cross sections were measured for 11 nuclei from 9Be to 209Bi by direct neutron-multiplicity sorting with a flat-efficiency neutron detector toward a goal of resolving the long-standing discrepancy between the Livermore and Saclay data. We present γSFs for the Ni isotopic chain and GDR cross sections for 159Tb as well as those updated for 209Bi.

Carbon-enhanced metal-poor (CEMP) r/s-stars show surface-abundance distributions characteristic of the so-called intermediate neutron capture process (i-process) of nucleosynthesis. We previously showed that the ingestion of protons in the convective helium-burning region of a low-mass low-metallicity star can explain the surface abundance distribution observed in CEMP r/s stars relatively well. Such an i-process requires detailed reaction network calculations involving hundreds of nuclei for which reaction rates have not yet been determined experimentally. We investigate the nuclear physics uncertainties affecting the i-process during the AGB phase of low-metallicity low-mass stars by propagating the theoretical uncertainties in the radiative neutron capture cross sections, as well as the 13C(a,n)16O reaction rate, and estimating their impact on the surface-abundance distribution. It is found that considering systematic uncertainties on the various nuclear ingredients affecting the radiative neutron capture rates, surface elemental abundances are typically predicted within +/-0.4 dex. The 56 < Z < 59 region of the spectroscopically relevant heavy-s elements of Ba-La-Ce-Pr as well as the r-dominated Eu element remain relatively unaffected by nuclear uncertainties. In contrast, the inclusion of the direct capture contribution impacts the rates in the neutron-rich A~45, 100, 160, and 200 regions, and the i-process production of the Z~45 and 65-70 elements. Uncertainties in the photon strength function also impact the overabundance factors by typically 0.2-0.4 dex. Nuclear level densities tend to affect abundance predictions mainly in the Z=74-79 regions. The uncertainties associated with the neutron-producing reaction 13C(a,n)16O and the unknown beta-decay rates are found to have a low impact on the overall surface enrichment, 9 pages, 8 Figures, A&A to be published

We present an on-going project consisting of analysis of a sample of twenty-five metal-poor stars, most of them carbon-enriched and thus tagged carbon-enhanced metal-poor (CEMP) stars, observed with the high-resolution HERMES spectrograph mounted on the Mercator telescope (La Palma), the UVES spectrograph on VLT (ESO Chile), or the HIRES spectrograph on KECK (Hawaii). This sample consists of CEMP-s stars, which are CEMP stars enriched in slow-neutron-capture (s-process) elements, as well as CEMP-rs stars enriched with both s-process and rapid-neutron-capture (r-process) elements. We also included an r-process-enriched star for comparison purposes. The origin of the abundance differences between CEMP-s and CEMP-rs stars is presently unknown. It has been claimed that the i-process (intermediate nucleosynthesis process), whose site still remains to be identified, could better reproduce CEMP-rs abundances than the s-process. We aim at understanding whether the i-process and its putative site can reproduce the abundance pattern measured in CEMP-rs stars., SCOPUS: ar.j, info:eu-repo/semantics/published

The radiative neutron capture rates for isotopes of astrophysical interest are commonly calculated within the statistical Hauser-Feshbach reaction model. Such an approach, assuming a high level density in the compound system, can be questioned in light and neutron-rich nuclei for which only a few or no resonant states are available. Therefore, in this work we focus on the direct neutron-capture process. We employ a shell-model approach in several model spaces with well-established effective interactions to calculate spectra and spectroscopic factors in a set of 50 neutron-rich target nuclei in different mass regions, including doubly-, semi-magic and deformed ones. Those theoretical energies and spectroscopic factors are used to evaluate direct neutron capture rates and to test global theoretical models using average spectroscopic factors and level densities based on the Hartree-Fock-Bogoliubov plus combinatorial method. The comparison of shell-model and global model results reveals several discrepancies that can be related to problems in level densities. All the results show however that the direct capture is non-negligible with respect to the by-default Hauser-Feshbach predictions and can be even 100 times more important for the most neutron-rich nuclei close to the neutron drip line., 10 pages, 9 figures, submitted to EPJ A

Among Carbon-Enhanced Metal-Poor (CEMP) stars, some are found to be enriched in s-process elements (CEMP-s), in r-process elements (CEMP-r) or in both s- and r-process elements (CEMP-rs). The origin of the abundance differences between CEMP-s and CEMP-rs stars is presently unknown. It has been claimed that the i-process, whose site still remains to be identified, could better reproduce CEMP-rs abundances than the s-process. We analyze high-resolution spectra of 25 metal-poor stars, observed with the high-resolution HERMES spectrograph mounted on the Mercator telescope, La Palma, or with the UVES/VLT and HIRES/KECK spectrographs. We propose a new, robust classification method for CEMP-s and CEMP-rs stars using eight heavy element abundances. The abundance profiles of CEMP-s and CEMP-rs stars are derived and there appears to be an abundance continuum between the two stellar classes. CEMP-rs stars present most of the characteristics of extrinsic stars such as CEMP-s, CH, Barium and extrinsic S stars, with an even larger binarity rate among CEMP-rs stars than among CEMP-s stars. Stellar evolutionary tracks of an enhanced carbon composition (consistent with our abundance determinations) are necessary to explain the position of CEMP-s and CEMP-rs stars in the HR diagram using Gaia DR2 parallaxes; they are found to lie mostly on the RGB. CEMP-rs stars can be explained as being polluted by a low-mass, low-metallicity TP-AGB companion experiencing i-process nucleosynthesis after proton ingestion during its first convective thermal pulses. The global fitting of our i-process models to CEMP-rs stars is as good as the one of our s-process models to CEMP-s stars. As such, CEMP-rs stars could be renamed as CEMP-sr stars, since they represent a particular manifestation of the s-process at low-metallicities. For these objects a call for an exotic i-process site may not necessarily be required anymore., 35 pages, 26 figures, Accepted for publication in A&A, Final version

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

A century ago, nuclear physics entered astrophysics, giving birth to a new field of science referred to as “Nuclear Astrophysics”. With time, it developed at an impressive pace into a vastly inter- and multidisciplinary field bringing into its wake not only astronomy and cosmology, but also many other sub-fields of physics, especially particle, solid-state and computational physics, as well as chemistry, geology and even biology. The present Astronuclear Physics review focusses primarily on the facets of nuclear physics that are of relevance to astronomy and astrophysics, the theoretical aspects being of special concern here. The observational aspects of astronomy and astrophysics that may have some connection to nuclear physics are only broadly reviewed, mainly through the provision of recent relevant references. Multi-messenger astronomy has developed most remarkably during the last decades, with often direct implications for nuclear astrophysics. The electromagnetic view of the components of the Universe has improved dramatically at all wavelengths, from the γ-ray to the radio domains, providing important new information on the Big Bang and the properties of stars. Neutrino astronomy has made giant steps forward. In particular, the famed “solar neutrino problem” is now behind us. The long-sought gravitational waves have at last been detected, with direct relevance namely to the merger of compact stars. The composition of Galactic Cosmic Rays and stellar/solar energetic particles is better known than ever, providing constrains on the GCR physics. On the stellar modeling side, we broadly brush the progress that has been made based on new observations, and even more so on the spectacular increase in computer capabilities. We briefly outline recent advances regarding the quiescent evolution of stars, as well as the eventual catastrophic supernova explosion of certain classes of them. In spite of significant improvements in the simulations, many long-standing problems still await solid solutions, particularly regarding the details and robustness of explosion simulations. In fact, new questions are continuously emerging, and new facts may endanger old ideas. The lion's share of this review concerns the nuclear physics phenomena that may be at work in astrophysical conditions, with a strong focus on theory. Exceptionally large varieties of nuclei have to be dealt with, ranging from the lightest to the heaviest ones, from the valley of nuclear stability all the way to the proton and neutron drip lines. An additional serious difficulty comes from the fact that the nuclei are immersed in highly unusual environments which may have a significant impact on their static properties, the diversity of their transmutation modes, some of which not being observable in the laboratory, and on the probabilities of these modes. The description of nuclei as individual entities has even to be replaced by the construction of an Equation of State at high enough temperatures and/or densities prevailing in the cores of exploding stars and in compact objects (neutron stars). The determination of a huge body of thermonuclear reaction cross sections is an especially challenging task, having to face the “world of almost no event” due to the smallness of the relative energies of charged-particle induced reactions relative to the Coulomb barriers, and/or the “world of exoticism”, as highly unstable nuclei are involved in several nucleosynthesis processes. The synthesis of the nuclides heavier than iron is briefly reviewed. Neutron capture mechanisms range from the s-process for the production of the stable nuclides located at the bottom of the valley of stability to the r-process responsible for the synthesis of the neutron-rich isobars. The origin of the neutron-deficient isobars observed in the SoS is attributed to the p-process. Emphasis is put on the astrophysics and nuclear physics uncertainties affecting the modeling of these nucleosynthesis mechanisms., SCOPUS: re.j, info:eu-repo/semantics/published

S stars are late-type giants with overabundances of s-process elements. They come in two flavours depending on the presence or not of technetium (Tc), an element without stable isotopes. Intrinsic S stars are Tc-rich and genuine asymptotic giant branch (AGB)stars while extrinsic S stars owe their s-process overabundances to the pollution from a former AGB companion, now a white dwarf(WD). In addition to Tc, another distinctive feature between intrinsic and extrinsic S stars is the overabundance of niobium (Nb) in the latter class. We discuss the case of the S stars BD+79 156 and o1Ori whose specificity is to share the distinctive features of both intrinsic and extrinsic S stars, namely the presence of Tc along with a Nb overabundance. BD+79 156 is the first clear case of a bitrinsic star, i.e. a doubly s-process-enriched object, first through mass transfer in a binary system, and then through internal nucleosynthesis (responsible for the Tc-enrichment in BD+79 156 which must therefore have reached the AGB phase of its evolution). This hybrid nature of the s-process pattern in BD+79 156 is supported by its binary nature and its location in the HR diagram just beyond the onset of the third dredge-up on the AGB. The Tc-rich, binary S-star o1Ori with a WD companion was another long-standing candidate for a similar hybrid s-process enrichment. However the marginal overabundance of Nb derived ino1Ori does not allow to trace unambiguously the evidence of a large pollution coming from the AGB progenitor of its current WD companion. As a side product, the current study offers a new way of detecting binary AGB stars with WD companions by identifying their Tc-rich nature along with a Nb overabundance., Comment: A & A Letters, accepted for publication

The Coordinated Research Project (CRP) with the code F41032 has been launched by the International Atomic Energy Agency (IAEA) in 2016 as a 5-year project with the scientific goal being two-fold: 1) updating the 2000 photonuclear data library and 2) constructing a reference database of photon strength functions. We report the experimental technique and methodology used for the former goal and selected giant-dipole resonance (GDR) data updated in the IAEA-CRP.

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.

A high-resolution study of the electromagnetic response of 206Pb below the neutron separation energy is performed using a γ→,γ′) experiment at the HIγ→S facility. Nuclear resonance fluorescence with 100% linearly polarized photon beams is used to measure spins, parities, branching ratios, and decay widths of excited states in 206Pb from 4.9 to 8.1 MeV. The extracted ΣB(E1)↑ and ΣB(M1)↑ values for the total electric and magnetic dipole strength below the neutron separation energy are 0.9±0.2 e2fm2 and 8.3±2.0μN 2, respectively. These measurements are found to be in very good agreement with the predictions from an energy-density functional (EDF) plus quasiparticle phonon model (QPM). Such a detailed theoretical analysis allows to separate the pygmy dipole resonance from both the tail of the giant dipole resonance and multi-phonon excitations. Combined with earlier photonuclear experiments above the neutron separation energy, one extracts a value for the electric dipole polarizability of 206Pb of αD=122±10 mb/MeV. When compared to predictions from both the EDF+QPM and accurately calibrated relativistic EDFs, one deduces a range for the neutron-skin thickness of Rskin 206=0.12–0.19 fm and a corresponding range for the slope of the symmetry energy of L=48–60 MeV. This newly obtained information is also used to estimate the Maxwellian-averaged radiative cross section Pb205(n,γ)Pb206 at 30 keV to be σ=130±25 mb. The astrophysical impact of this measurement—on both the s-process in stellar nucleosynthesis and on the equation of state of neutron-rich matter—is discussed., SCOPUS: ar.j, info:eu-repo/semantics/published

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.

Closed-form models for photon strength functions for the description of photoabsorption cross section in the energy range 5 - 30 MeV for even-even nuclei are tested. The experimental database was prepared with systematic uncertainty less than 10% from the EXFOR data. The uncertainties are estimated using the calculations of the photo cross sections within TALYS 1.6 code. The theoretical models are compared with experimental photoabsorption cross section data. The minimum of the least-square deviation and the root-mean-square deviation factor are used as a criteria comparison of the theoretical calculations with experimental data. It is shown that the simple modified Lorentzian model is the best approach for simulation of the photoabsorption cross section at the gamma-ray energies below ~ 30 MeV., SCOPUS: ar.j, info:eu-repo/semantics/published

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

Context. S stars are late-type giants with spectra showing characteristic molecular bands of ZrO in addition to the TiO bands typical of M stars. Their overabundance pattern shows the signature of s-process nucleosynthesis. Intrinsic, technetium (Tc)-rich S stars are the first objects on the asymptotic giant branch (AGB) to undergo third dredge-up (TDU) events. Exquisite Gaia parallaxes now allow for these stars to be precisely located in the Hertzsprung-Russell (HR) diagram. Here we report on a population of low-mass, Tc-rich S stars previously unaccounted for by stellar evolution models. Aims. Our aim is to derive parameters for a sample of low-mass, Tc-rich S stars and then, by comparing their location in the HR diagram with stellar evolution tracks, to derive their masses and to compare their measured s-process abundance profiles with recently derived STAREVOL nucleosynthetic predictions for low-mass AGB stars. Methods. Stellar parameters were obtained using a combination of HERMES high-resolution spectra, accurate Gaia Data Release 2 (Gaia-DR2) parallaxes, stellar-evolution models, and newly designed MARCS model atmospheres for S-type stars. Results. We report on six Tc-rich S stars lying close to the 1 M ⊙ (initial mass) tracks of AGB stars of the corresponding metallicity and above the predicted onset of TDU, as expected. This provides direct evidence for TDUs occurring in AGB stars with initial masses as low as ∼1 M⊙ and at low luminosity, that is, at the start of the thermally pulsing AGB. We present AGB models producing TDU in those stars with [Fe/H] in the range -0.25 to -0.5. There is reasonable agreement between the measured and predicted s-process abundance profiles. For two objects however, CD -29°5912 and BD +34°1698, the predicted C/O ratio and s-process enhancements do not simultaneously match the measured ones., SCOPUS: ar.j, info:eu-repo/semantics/published

The theory of the nuclear energy-density functional is used to provide a unified and thermodynamically consistent treatment of all regions of cold non-accreting neutron stars. In order to assess the impact of our lack of complete knowledge of the density dependence of the symmetry energy on the constitution and the global structure of neutron stars, we employ four different functionals. All of them were precision fitted to essentially all the nuclear-mass data with the Hartree-Fock-Bogoliubov method and two different neutron-matter equations of state based on realistic nuclear forces. For each functional, we calculate the composition, the pressure-density relation, and the chemical potentials throughout the star. We show that uncertainties in the symmetry energy can significantly affect the theoretical results for the composition and global structure of neutron stars. To facilitate astrophysical applications, we construct analytic fits to our numerical results., 36 pages, 31 figures, 29 tables; corrected according to an erratum (2019, accepted)

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 role of the symmetry energy on the internal constitution and the global structure of a cold nonaccreted neutron star is studied using a set of unified equations of state. Based on the nuclear energy-density functional theory, these equations of state provide a thermodynamically consistent treatment of all regions of the star and were calculated using the four different Brussels-Montreal functionals BSk22, BSk24, BSk25 and BSk26. Our predictions are compared to various constraints inferred from astrophysical observations including the recent detection of the gravitational wave signal GW170817 from a binary neutron-star merger., SCOPUS: cp.p, info:eu-repo/semantics/published

Nuclear level densities (NLDs) and \(\gamma \)-ray strength functions (\(\gamma \)SFs) of \(^{91,92}\)Zr have been extracted from particle-\(\gamma \) coincidences using the Oslo method. The extracted \(\gamma \)SF data, combined with photonuclear cross sections, cover the whole energy range from \(E_{\gamma } \approx 1.5\) MeV up to the giant dipole resonance at \(E_{\gamma } \approx 17\) MeV. The wide-range \(\gamma \)SF data display structures at \(E_{\gamma } \approx 9.5\) MeV, compatible with a superposition of the spin-flip M1 resonance and a pygmy E1 resonance. Furthermore, the \(\gamma \)SF shows a minimum at \(E_{\gamma } \approx \) 2–3 MeV and an increase at lower \(\gamma \)-ray energies. The experimentally constrained NLDs and \(\gamma \)SFs are shown to reproduce known (\(n, \gamma \)) and Maxwellian-averaged cross sections for \(^{91,92}\)Zr using the TALYS reaction code, thus serving as a benchmark for this indirect method of estimating (\(n, \gamma \)) cross sections for Zr isotopes.

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

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.

Context. S stars are transition objects between M-type giants and carbon stars on the asymptotic giant branch (AGB). They are characterized by overabundances of s-process elements. Roughly half of them are enhanced in technetium (Tc), an s-process element with no stable isotope, while the other half lack technetium. This dichotomy arises from the fact that Tc-rich S stars are intrinsically producing s-process elements and have undergone third dredge-up (TDU) events, while Tc-poor S stars owe their s-process overabundances to a past pollution by a former AGB companion which is now an undetected white dwarf, and since the epoch of the mass transfer, technetium has totally decayed. Aims. Our aim is to analyse the abundances of S stars and gain insights into their evolutionary status and on the nucleosynthesis of heavy s-process elements taking place in their interior. In particular, the location of extrinsic and intrinsic S stars in the HR diagram will be compared with the theoretical onset of the TDU on the thermally pulsing AGB. Methods. A sample of 19 S-type stars was analysed by combining HERMES high-resolution spectra, accurate Gaia Data Release 2 (GDR2) parallaxes, stellar-evolution models, and newly designed MARCS model atmospheres for S-type stars. Various stellar parameters impact the atmospheric structure of S stars, not only effective temperature, gravity, metallicity and microturbulence but also C/O and [s/Fe]. We show that photometric data alone are not sufficient to disentangle these parameters. We present a new automatic spectral-fitting method that allows one to constrain the range of possible atmospheric parameters. Results. Combining the derived parameters with GDR2 parallaxes allows a joint analysis of the location of the stars in the Hertzsprung-Russell diagram and of their surface abundances. For all 19 stars, Zr and Nb abundances are derived, complemented by abundances of other s-process elements for the three Tc-rich S stars. These abundances agree within the uncertainties with nucleosynthesis predictions for stars of corresponding mass, metallicity and evolutionary stage. The Tc dichotomy between extrinsic and intrinsic S stars is seen as well in the Nb abundances: Intrinsic, Tc-rich S stars are Nb-poor, whereas extrinsic, Tc-poor S stars are Nb-rich. Most extrinsic S stars lie close to the tip of the red giant branch (RGB), and a few are located along the early AGB. All appear to be the cooler analogues of barium stars. Barium stars with masses smaller than 2.5 M⊙ turn into extrinsic S stars on the RGB, because only for those masses does the RGB tip extend to temperatures lower than ∼4200 K, which allows the ZrO bands distinctive of S-type stars to develop. On the contrary, barium stars with masses in excess of ∼2.5 M⊙ can only turn into extrinsic S stars on the E-AGB, but those are short-lived, and thus rare. The location of intrinsic S stars in the HR diagram is compatible with them being thermally-pulsing AGB stars. Although nucleosynthetic model predictions give a satisfactory distribution of s-process elements, fitting at the same time the carbon and heavy s-element enrichments still remains difficult. Finally, the Tc-rich star V915 Aql is challenging as it points at the occurrence of TDU episodes in stars with masses as low as M ∼ 1 M⊙, SCOPUS: ar.j, info:eu-repo/semantics/published

Context. Barium stars are s-process enriched giants. They owe their chemical peculiarities to a past mass transfer phase. During this phase they were polluted by their binary companion, which at the time was an asymptotic giant branch (AGB) star, but is now an extinct white dwarf. Barium stars are thus ideal targets for understanding and constraining the s-process in low-and intermediate-mass AGB stars. Aims. We derive the abundances of a large number of heavy elements in order to shed light on the conditions of operation of the neutron source responsible for the production of s-elements in the former companions of the barium stars. Methods. Adopting a recently used methodology, we analyse a sample of eighteen highly enriched barium stars observed with the high-resolution HERMES spectrograph mounted on the Mercator telescope (La Palma). We determine the stellar parameters and abundances using MARCS model atmospheres. In particular, we derive the Nb-Zr ratio which was previously shown to be a sensitive thermometer for the s-process nucleosynthesis. Indeed, in barium stars, 93Zr has fully decayed into mono-isotopic 93Nb, so Nb/Zr is a measure of the temperature-sensitive 93Zr/Zr isotopic ratio. Results. HD 28159, previously classified as K5III and initially selected to serve as a reference cool K star for our abundance analysis, turns out to be enriched in s-process elements, and as such is a new barium star. Four stars are characterised by high nitrogen abundances, and among those three have high [Nb/Zr] and [hs/ls] ratios. The derived Zr and Nb abundances provide more accurate constraints on the s-process neutron source, identified to be 13C(α, n)16O for barium stars. The comparison with stellar evolution and nucleosynthesis models shows that the investigated barium stars were polluted by a low-mass (M ∼ 2-3 M⊙) AGB star. HD 100503 is potentially identified as a high metallicity analogue of carbon-enhanced metal-poor star enriched in both r-and s-process elements (CEMP-rs)., SCOPUS: ar.j, info:eu-repo/semantics/published

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

The astrophysical p-process is an important way of nucleosynthesis to produce the stable and protonrich nuclei beyond Fe which can not be reached by the s- and r-processes. In the present study, the impact of nuclear ingredients, especially the nuclear potential, level density and strength function, to the astrophysical reaction rates of (p,γ), (α,γ), (γ,p), and (γ,α) reactions are systematically studied. The calculations are performed basad on the modern reaction code TALYS for about 3000 stable and proton-rich nuclei with 12≤Z≤110. In particular, both of the Wood-Saxon potential and the microscopic folding potential are taken into account. It is found that both the capture and photonuclear reaction rates are very sensitive to the nuclear potential, thus the better determination of nuclear potential would be important to reduce the uncertainties of reaction rates. Meanwhile, the Extreme Light Infrastructure-Nuclear Physics (ELI-NP) facility is being developed, which ill provide the great opportunity to experimentally study the photonuclear reactions in p-process. Simulations of the experimental setup for the measurements of the photonuclear reactions 96Ru(γ,p) and 96Ru(γ,α) are performed. It is shown that the experiments of photonuclear reactions in p-process based on ELI-NP are quite promising., SCOPUS: cp.p, info:eu-repo/semantics/published

S-type stars are late-type giants enhanced with s-process elements originating either from nucleosynthesis during the Asymptotic Giant Branch (AGB) or from a pollution by a binary companion. The former are called intrinsic S stars, and the latter extrinsic S stars. The intrinsic S stars are on the AGB and have undergone third dredge-up events. The atmospheric parameters of S stars are more numerous than those of M-type giants (C/O ratio and s-process abundances affect the thermal structure and spectral synthesis), and hence they are more difficult to derive. These atmospheric parameters are also entangled within each other. Nevertheless, high-resolution spectroscopic data of S stars combined with the Gaia Data Release 2 (GDR2) parallaxes and with the MARCS model atmospheres for S-type stars were used to derive effective temperatures, surface gravities, and luminosities. These parameters not only allow to locate the intrinsic and extrinsic S stars in the Hertzsprung-Russell (HR) diagram but also allow the accurate abundance analysis of the s-process elements., SCOPUS: ar.k, info:eu-repo/semantics/published

Context. X-ray observations of soft X-ray transients in quiescence suggest the existence of heat sources in the crust of accreted neutron stars. Heat is thought to be released by electroweak and nuclear processes triggered by the burying of ashes of X-ray bursts. Aims. The heating in the crust of accreting neutron stars is studied using a fully quantum approach taking consistently into account nuclear shell effects. Methods. To this end, we have followed the evolution of ashes made of 56 Fe employing the nuclear energy-density functional theory. Both the outer and inner crusts are described using the same functional, thus ensuring a unified and thermodynamically consistent treatment. To assess the role of accretion on the structure of the crust, we have employed the set of accurately calibrated Brussels-Montreal functionals BSk19, BSk20, and BSk21, for which the equations of state of nonaccreted neutron stars have been already calculated. These energy-density functionals were fitted to the same set of nuclear masses but were simultaneously adjusted to realistic neutron-matter equations of state with different degrees of stiffness at suprasaturation densities. For comparison, we have also considered the SLy4 functional. Results. Due to nuclear shell effects, the interior of fully accreted crust is found to be much less stratified than in previous studies. In particular, large regions of the inner crust contain clusters with the magic number Z = 14. The heat deposited in the outer crust is tightly constrained by experimental atomic mass data. The shallow heating we obtain does not exceed 0.2 MeV per accreted nucleon and is therefore not enough to explain the cooling of some soft X-ray transients. The total heat released in the crust is very sensitive to details of the nuclear structure and is predicted to lie in the range from 1.5 MeV to 1.7 MeV per accreted nucleon. Conclusions. The evolution of an accreted matter element and therefore the location of heat sources are governed to a large extent by the existence of nuclear shell closures. Ignoring these effects in the inner crust, the total heat falls to ∼0.6 MeV per accreted nucleon., SCOPUS: ar.j, 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.

Photodisintegration reaction rates involving charged particles are relevant to the p-process nucleosynthesis that aims at explaining the production of stable neutron-deficient nuclides heavier than iron. In this study, considering the compound and pre-equilibrium reaction mechanisms, the cross sections and astrophysical rates of (γ,p) and (γ,α) reactions for about 3000 target nuclei with 10≤Z≤100 ranging from stable to proton dripline nuclei are computed. To study the sensitivity of the calculations to the optical model potentials (OMPs), both the phenomenological Woods-Saxon and the microscopic folding OMPs are taken into account. The systematic comparisons show that the reaction rates, especially for the (γ,α) reaction, are dramatically influenced by the OMPs. Thus, better determination of the OMP is crucial to reduce the uncertainties of the photodisintegration reaction rates involving charged particles. Meanwhile, a γ-beam facility at Extreme Light Infrastructure-Nuclear Physics (ELI-NP) is being developed which will open new opportunities to experimentally study the photodisintegration reactions of astrophysical interest. Considering both the important reactions identified by the nucleosynthesis studies and the purpose of complementing the experimental results for the reactions involving p nuclei, the measurements of six (γ,p) and eight (γ,α) reactions based on the γ-beam facility and the Extreme Light Infrastructure Silicon Strip Array (ELISSA) for the detection of charged particles at ELI-NP are proposed. Furthermore, the geant4 simulations on these (γ,p) and (γ,α) reactions are performed using the calculated cross sections and the features of the γ-beam facility and the ELISSA detector at ELI-NP. Simultaneously satisfying the minimum detectable limit of the experimental yield and the particle identification of protons and α particles, the minimum required energies of the γ beam to measure the six (γ,p) and eight (γ,α) reactions are estimated. It is shown that the direct measurements of these photonuclear reactions based on the γ-beam facility at ELI-NP within the Gamow windows at the typical temperature of T9=2.5 for the p-process are fairly feasible and promising. We believe that this pivotal work will guide the future photodisintegration experiments at ELI-NP. Furthermore, the expected experimental results will be used to constrain the OMPs of the charged particles, which can eventually reduce the uncertainties of the reaction rates for the p-process nucleosynthesis., SCOPUS: ar.j, info:eu-repo/semantics/published

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 production of super-heavy transuranium elements by stellar nucleosynthesis processes remains an open question. The most promising process that could potentially give rise to the formation of such elements is the so-called rapid neutron-capture process, or r-process, known to be at the origin of approximately half of the A > 60 stable nuclei observed in nature. However, despite important efforts, the astrophysical site of the r-process remains unidentified. Here, we study the r-process nucleosynthesis in material that is dynamically ejected by tidal and pressure forces during the merging of binary neutron stars. Neutron star mergers could potentially be the dominant r-process site in the Galaxy, but also due to the extreme neutron richness found in such environment, could potentially synthesise super-heavy elements. R-process nucleosynthesis during the decompression is known to be largely insensitive to the detailed astrophysical conditions because of efficient fission recycling, producing a composition that closely follows the solar r-abundance distribution for nuclei with mass numbers A > 140 . During the neutron irradiation, nuclei up to charge numbers Z ≃ 110 and mass number A ≃ 340 are produced, with a major peak production at the N = 184 shell closure, i.e. around A ≃ 280 . Super-heavy nuclei with Z > 110 can hardly be produced due to the efficient fission taking place along those isotopic chains. Long-lived transuranium nuclei are inevitably produced by the r-process. The predictions concerning the production of transuranium nuclei remain however very sensitive to the predictions of fission barrier heights for such super-heavy nuclei. More nuclear predictions within different microscopic approaches are needed.

Partial cross sections of the 89 Y(p, ) 90 Zr reaction have been measured to investigate the -ray strength function in the neutron-magic nucleus 90 Zr. For five proton energies between Ep = 3:65 MeV and Ep = 4:70 MeV, partial cross sections for the population of seven discrete states in 90 Zr have been determined by means of in-beam -ray spectroscopy. Since these -ray transitions are dominantly of E1 character, the present measurement allows an access to the low-lying dipole strength in 90 Zr. A -ray strength function based on the experimental data could be extracted, which is used to describe the total and partial cross sections of this reaction by Hauser-Feshbach calculations successfully. Significant di erences with respect to previously measured strength functions from photoabsorption data point towards deviations from the Brink-Axel hypothesis relating the photo-excitation and de-excitation strength functions.