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The impact of low-energy multipole excitations and pygmy resonances on radiative neutron and proton-capture cross sections in nuclei close to the β-stability line is investigated. For this purpose, a microscopic theoretical approach based on self-consistent density functional theory and quasiparticle-random-phase-approximation formalism extended with multiphonon degrees of freedom is implemented in a statistical reaction model. The advantage of the method is the microscopic nuclear structure input for unified description of low-energy multiphonon excitations and pygmy and giant resonances. This is found to be important for the understanding of the fine structure and dynamics of the nuclear response function at low energies, which strongly influences nuclear reaction rates of astrophysical relevance. Calculations of the radiative capture cross sections of the reactions 85Kr(n,γ)86Kr, 87Sr(n,γ)88Sr, and Y89(p,γ)90Zr are discussed in comparison with experimental data. For the reactions 89Zr(n,γ)90Zr and 91Mo(n,γ)92Mo theoretical predictions of the reaction cross sections are made. [ABSTRACT FROM AUTHOR]

The neutron capture reaction is investigated. The three major reaction mechanisms, namely, compound-nucleus capture (CNC), pre-equilibrium capture (PEC), and direct capture (DIC), are considered on the basis of the Hauser-Feshbach model, the exciton model, and potential model, respectively. The three mechanisms are treated simultaneously and consistently, i.e, they are obtained on the basis of the same nuclear ingredients, such as the optical potential and nuclear-level densities. In this framework, the three components are calculated on the same footing and represent partial fluxes of the same total reaction cross section. The total neutron-capture cross sections and astrophysical reaction rates are calculated within the updated modern reaction code talys for about 8000 nuclei with 8 < Z < 110 lying between the proton and neutron drip lines. The nuclear-structure ingredients involved in the calculation are determined from experimental data whenever available and, if not, from global microscopic nuclear models. For the targets with mass number A > 26, a fair agreement between the computed total-capture cross sections and experimental data is found but, for the lightest nuclei, only the predicted DIC cross sections reproduce the experimental results satisfactorily. Significant and even dominant contribution to the total reaction rate comes from the DIC component for neutron-rich nuclei, especially in the Z = 50-70 region. The impact of the newly determined reaction rates on the r process abundances resulting from the ejection of matter in neutrino-driven winds or the decompression of neutron star matter is investigated. [ABSTRACT FROM AUTHOR]

Some 27 Hartree-Fock-Bogoliubov (HFB) mass models have been developed by the Brussels-Montreal collaboration. Each of these models has been obtained with different model prescriptions or corresponds to a significantly different minimum in the parameter space. The corresponding uncertainties in the mass extrapolation are discussed. In addition, for each of these models, uncertainties associated with local variations of the model parameters exist. Those are estimated for the HFB-24 mass model using a variant of the backward-forward Monte Carlo method to propagate the uncertainties on the masses of exotic nuclei far away from the experimentally known regions. The resulting uncertainties are found to be significantly lower than those arising from the 27 HFB mass models. In addition, the derived correlations between the calculated masses and between model parameters are analyzed. [ABSTRACT FROM AUTHOR]

Neutron star (NS) merger ejecta offer a viable site for the production of heavy r-process elements with nuclear mass numbers A ≳ 140. The crucial role of fission recycling is responsible for the robustness of this site against many astrophysical uncertainties, but calculations sensitively depend on nuclear physics. In particular, the fission fragment yields determine the creation of 110 ≲ A ≲ 170 nuclei. Here, we apply a new scission-point model, called SPY, to derive the fission fragment distribution (FFD) of all relevant neutron-rich, fissioning nuclei. The model predicts a doubly asymmetric FFD in the abundant A ≃278 mass region that is responsible for the final recycling of the fissioning material. Using ejecta conditions based on relativistic NS merger calculations, we show that this specific FFD leads to a production of the A ≃ 165 rare-earth peak that is nicely compatible with the abundance patterns in the Sun and metal-poor stars. This new finding further strengthens the case of NS mergers as possible dominant origin of r nuclei with A ≳ 140. [ABSTRACT FROM AUTHOR]

We present a new Hartree-Fock-Bogoliubov nuclear mass model based on standard forms of Skyrme and pairing functionals, which corresponds to the most accurate mass model we ever achieved within the framework of the nuclear energy density functional theory. Our new mass model is characterized by a model standard deviation smod=0.500 MeV with respect to essentially all the 2353 available mass data for nuclei with neutron and proton numbers larger than 8. At the same time, the underlying Skyrme functional yields a realistic description of infinite homogeneous nuclear matter properties, as determined by realistic calculations and by experiments; these include in particular the incompressibility coefficient, the pressure in charge-symmetric nuclear matter, the neutron-proton effective mass splitting, the stability against spin and spin-isospin fluctuations, as well as the neutron-matter equation of state. [ABSTRACT FROM AUTHOR]

Our family of three Hartree-Fock-Bogoliubov (HFB) mass models, labeled BSk19, BSk20, and BSk21, is here extended by (a) refitting to the 2012 Atomic Mass Evaluation (AME), and (b) varying the symmetry coefficient J. Five new models, labeled BSk22 to BSk26, along with their mass tables, HFB-22 to HFB-26, respectively, are presented. These models are characterized by unconventional Skyrme forces containing r4 and i5 terms, i.e., density-dependent generalizations of the usual t\ and t2 terms, respectively. Highly realistic contact pairing forces are used. The Skyrme forces are constrained to fit realistic equations of state of neutron matter stiff enough to support the massive neutron stars PSR J1614--2230 and PSR J0348 + 0432. Unphysical spin and spin-isospin instabilities of homogeneous nuclear matter, including the transition to a polarized state in neutron-star matter, are eliminated with the new forces. The best fits to the new database of 2353 nuclei are found for models BSk24 ( J = 30 MeV) and BSk25 (J = 29 MeV), for which the root-mean square (rms) deviations are 0.55 and 0.54 MeV, respectively. Despite the larger database this is even better than the rms deviation of 0.58 MeV that we found with our fits to the 2003 AME. With J = 32 MeV the rms deviation rises to 0.63 MeV. The neutron-skin thicknesses derived from antiproton scattering are shown to be consistent with the conclusions that we have drawn from masses. [ABSTRACT FROM AUTHOR]

Photoneutron cross sections were measured for 94Mo, 95Mo, 96Mo, 97Mo, 98Mo, and 100Mo near the neutron threshold with quasi-monochromatic laser-Compton scattering γ rays. The photoneutron data were analyzed with the Skyrme Hartree-Fock-Bogoliubov (HFB) plus quasiparticle random phase approximation (QRPA) model and the axially symmetric-deformed Gogny HFB plus QRPA model of El γ-ray strength. Combining the γ-ray strength function constrained by the present photoneutron data with either the nuclear resonance fluorescence data or the updated Oslo data to supplement the data below the neutron threshold, a thorough analysis of the reverse (n,γ) cross sections is made whenever measurements are available. The Oslo data and the corresponding uncertainties are updated based on the latest results of the S-wave neutron spacing and the average radiative width determined in particular for 96Mo. Finally, radiative neutron capture cross sections for two radioactive nuclei, 93Mo and 99Mo, are deduced with the γ-ray strength function method. [ABSTRACT FROM AUTHOR]

Large-scale calculations of the E\ strength are performed within the random phase approximation (RPA) based on the relativistic point-coupling mean field approach in order to derive the radiative neutron capture cross sections for all nuclei of astrophysical interest. While the coupling to the single-particle continuum is taken into account in an explicit and self-consistent way, additional corrections like the coupling to complex configurations and the temperature and deformation effects are included in a phenomenological way to account for a complete description of the nuclear dynamical problem. It is shown that the resulting £1-strength function based on the PCF1 force is in close agreement with photoabsorption data as well as the available experimental E\ strength data at low energies. For neutron-rich nuclei, as well as light neutron-deficient nuclei, a low-lying so-called pygmy resonance is found systematically in the 5-10 MeV region. The corresponding strength can reach 10% of the giant dipole strength in the neutron-rich region and about 5% in the neutron-deficient region, and is found to be reduced in the vicinity of the shell closures. Finally, the neutron capture reaction rates of neutron-rich nuclei is found to be about 2-5 times larger than those predicted on the basis of the nonrelativistic RPA calculation and about a factor 50 larger than obtained with traditional Lorentzian-type approaches. [ABSTRACT FROM AUTHOR]

Primary &ggr;-ray spectra for a wide excitation-energy range have been extracted for 44Ti from particle-y coincidence data of the 46Ti(p,t&ggr;)44Ti reaction. These spectra reveal information on the &ggr;-decay pattern of the nucleus and may be used to extract the level density and radiative strength function applying the Oslo method. Models of the level density and radiative strength function are used as input for cross-section calculations of the 40Ca(&agr;,&ggr;)44Ti reaction. Acceptable models should reproduce data on the 40Ca(&agr;,&ggr;)44Ti reaction cross section as well as the measured primary &ggr;-ray spectra. This is only achieved when a coherent normalization of the slope of the level density and radiative strength function is performed. Thus, the overall shape of the experimental primary &ggr;-ray spectra puts a constraint on the input models for the rate calculations. [ABSTRACT FROM AUTHOR]

Photoneutron cross sections were measured for 118Sn, 119Sn, 120Sn, 122Sn, 124Sn near neutron threshold with quasi-monochromatic laser-Compton scattering γ rays. A systematic analysis of the present photoneutron data and existing neutron-capture data is made using the y-ray strength function on the basis of the HFB + QRPA model of E1 strength supplemented with a pygmy dipole resonance, which was deduced from a previous study on 116Sn and 117Sn. Radiative neutron capture cross sections for two radioactive nuclei, 121Sn and 123Sn, are deduced through the y-ray strength function method. [ABSTRACT FROM AUTHOR]

The correlation between the pygmy dipole strength and the symmetry energy of nuclear matter is reanalyzed. While previous calculations [ A. Klimkiewicz et al. Phys. Rev. C 76 051603 (2007) A. Carbone, G. Colò, A. Bracco, L.-G. Cao, P. F. Bortignon, F. Camera and O. Wieland Phys. Rev. C 81 041301 (2010)] have clearly shown a direct correlation between both quantities, it remains unclear to what extent experimental as well as theoretical uncertainties can allow for an accurate determination of the symmetry energy. For this reason, we have recalculated the low-lying strength distributions of the giant dipole resonances for 130Sn and 132Sn that have been recently measured, taking into account the above uncertainties. The calculations are performed within two microscopic models, namely, the discrete quasiparticle random phase approximation (DRPA) and the quasiparticle continuum RPA, which is an extension of the DRPA that takes the coupling to the single-particle continuum into account in an exact way. [ABSTRACT FROM AUTHOR]

We have calculated the zero-temperature properties of the outer crust of neutron stars for four nuclear-mass models based on the Hartree-Fock-Bogoliubov method: the three most recent Skyrme-force models (HFB-19, HFB-20, and HFB-21) and the Gogny-force model D1M. While the equation of state is substantially the same for the four models, the nuclidic composition varies considerably from one model to another. We solve the Tolman-Oppenheimer-Volkoff equations by integrating inward from the surface and thereby determine the abundance of each nuclide in the outer crust of a typical neutron star of mass 1.5M☉ and radius 13 km. Although the total mass of the outer crust is slightly model dependent, its thickness is essentially the same for all four models. [ABSTRACT FROM AUTHOR]

The E1 strength function for 15 stable and unstable Sn even-even isotopes from A = 100 to A = 176 are calculated using a self-consistent microscopic theory which, in addition to the standard (quasiparticle) random-phase approximation [(Q)RPA] approach, takes into account phonon coupling and the single-particle continuum (by means of the discretization procedure) with a cutoff of 100 MeV. Our analysis shows two distinct regions for which the integral characteristics of both the giant and pygmy resonances behave rather differently. For neutron-rich nuclei, starting from 132Sn, we obtain a giant E1 resonance which significantly deviates from the widely used systematics extrapolated from experimental data in the β-stability valley. We show that the inclusion of phonon coupling is necessary for a proper description of the low-energy pygmy resonances and the corresponding transition densities for A < 132 nuclei, while in the A > 132 region the influence of phonon coupling is significantly smaller. The radiative neutron capture cross sections leading to the stable 124Sn and unstable 132Sn and 150Sn nuclei are calculated with both the (Q)RPA and the beyond-(Q)RPA strength functions and shown to be sensitive to both the predicted low-lying strength and the phonon-coupling contribution. The comparison with the widely used phenomenological generalized Lorentzian approach shows considerable differences both for the strength function and the radiative neutron capture cross section. In particular, for the neutron-rich 150Sn, the reaction cross section is found to be increased by a factor greater than 20. We conclude that the present approach may provide a complete and coherent description of the γ-ray-strength function for astrophysics applications. In particular, such calculations are highly recommended for a reliable estimate of the electromagnetic properties of exotic nuclei. [ABSTRACT FROM AUTHOR]

Mean-field calculations can now 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 the TALYS reaction code to improve the predictions of neutron-induced fission cross sections. 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 on the experimental data available for the uranium isotopic chain. It is also shown that the various inputs can be tuned to reproduce, at best, experimental data in one unique coherent framework, so that in a close future it should become possible to make, on the basis of such models, accurate fission-cross-section calculations and the corresponding estimates for nuclei, energy ranges, or reaction channels for which no data exist. Such model uncertainties are usually not taken into account in data evaluations. [ABSTRACT FROM AUTHOR]

Viable theoretical predictions of photon strength functions (PSFs) covering the whole nuclear chart are of great interest for different nuclear applications, including, in particular, nuclear astrophysics. Recently, such a global PSF model consisting of axially deformed Hartree-Fock-Bogolyubov (HFB) + quasiparticle random phase approximation (QRPA) calculations with the D1M Gogny interaction and a phenomenological low-energy contribution was proposed. In the present paper, we test this model predictions against previously published data from measurements of multistep ? cascades following neutron capture on isolated resonances performed with the DANCE detector. Such data present a stringent test of the PSFs models, in particular for the properties of the M1 scissors mode and the possible low-energy PSFs enhancement. A detailed comparison is made for spectra obtained from resonances for spherical, quasispherical, and well-deformed nuclei. This comparison indicates that 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 photoabsorption PSF, should be present in all nuclei. A systematics of this low-energy contribution, assumed in the M1 PSF, is proposed. [ABSTRACT FROM AUTHOR]

We present an upgraded version of the SPY model, called SPY2 for version 2 of the scission point yield, to estimate mainly the yields and the kinetic energy distributions of fission fragments: The theoretical framework is similar to our previous version, i.e., a statistical scission point model, but this version is based on fully microscopic nuclear ingredients describing the fragments properties at the scission point. These include the static properties 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 been extended to the proton density distribution and the nuclear states densities. Considering realistic proton densities of fragments allows us to improve the definition of the scission point as well as the prediction of the kinetic energy distribution and to link the kinetic energy to the diffuseness of the fragments' proton density. New microscopic nuclear states densities improve the general coherence of the model, in particular regarding the inclusion of the odd-even pairing effect. In this updated SPY2 version, the calculation of the fission yields and kinetic energy distributions is significantly improved and found to be in relatively good agreement with experiments, 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 the fission mode as well as mean fragments deformation and total kinetic energies has been performed for some 2000 fissioning nuclei with 78 = Z = 110 lying between the proton and neutron drip lines. [ABSTRACT FROM AUTHOR]

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 on the basis of experimental and theoretical information on the E1 and M1 strength functions, inspired both from axially deformed quasiparticle random-phase approximation and shell-model calculations, we derive simple expressions to determine systematically the dipole strength in order to update former prescriptions with a special emphasis on new expressions for the M1 spin-flip and scissors modes. 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 is obtained. Its impact on the total radiative width as well as radiative neutron dure cross sections is also discussed. The new expressions are believed to represent an improvement with respect to the analytical systematics proposed in the past and used traditionally in reaction codes, such as the recommended ripl-3 prescriptions. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Valuable theoretical predictions of nuclear dipole excitations in the whole nuclear chart are of great interest for different 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 deexcitation strength function. To do so, shell-model calculations of the deexcitation dipole strength function are performed and their limit at low γ energies used to complement phenomenologically the QRPA calculations. We compare our final prediction of the E1 and M1 strength with available experimental data at low energies and show that a fairly good agreement is obtained. Predictions of the dipole strength function for spherical and deformed nuclei within the valley of β stability as well as in the neutron-rich region are discussed and compared with traditional Lorentzian-type prescriptions. Its impact on the total radiative width as well as radiative neutron and proton capture cross sections is studied. [ABSTRACT FROM AUTHOR]

Nuclear level densities (NLDs) and γ-ray strength functions (γSFs) have been extracted from particle-γ coincidences of the 92Zr(p,p'γ)92Zr and 92Zr(p,dγ)91Zr reactions using the Oslo method. The new 91,92Zr γSF data, combined with photonuclear cross sections, cover the whole energy range from Eγ ≈ 1.5 MeV up to the giant dipole resonance at Eγ ≈ 17 MeV. The wide-range γSF data display structures at Eγ ≈ 9.5 MeV, compatible with a superposition of the spin-flip M1 resonance and a pygmy E1 resonance. Furthermore, the γ SF shows a minimum at Eγ ≈ 2-3 MeV and an increase at lower γ-ray energies. The experimentally constrained NLDs and γSFs are shown to reproduce known (n,γ) and Maxwellian-averaged cross sections for 91,92Zr using the talys reaction code, thus serving as a benchmark for this indirect method of estimating (n,γ) cross sections for Zr isotopes. [ABSTRACT FROM AUTHOR]

The average resonance capture (ARC) data measured at different filter beam facilities are re-analyzed. They include all measurements made between 1970 and 1990, but only partially exploited. Updated spectroscopic information on the states of interest as well as on s -wave resonance spacing are used to extract the E1 and M1 photon strength function. This re-evaluation aims at providing experimental information on the E1 and M1 strength function around the neutron binding energy and in doing so provides also constraints for existing models used in statistical reaction codes. The revised data are compared to the photon strength function extracted from other experimental methods, such as photoneutron data and Oslo-method data. We also compare the ARC data with recent quasiparticle random phase approximation calculations based on the D1M Gogny force. The ratio of the E1 to M1 strength functions is also analyzed and proposed as a new stringent test for the future elaboration of theoretical models for the dipole strength function. [ABSTRACT FROM AUTHOR]

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 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 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 ß stability as well as in the neutron-rich region are discussed. Its impact on the radiative neutron capture cross section is also analyzed. [ABSTRACT FROM AUTHOR]

Background: 92Mo is the most abundant nucleus of the p nuclei, with an isotopic abundance of more than 14%. The γ-process nucleosynthesis is believed to produce 92Mo but fails to explain its large abundance, especially with respect to the other p nuclei produced in the same stellar environment. Further studies require precise nuclear models for the calculation of reaction cross sections. Purpose: A measurement of the total and partial cross sections of the 92Mo(p,γ)93Tc reaction allows for a stringent test of statistical-model predictions. Not only different proton+nucleus optical model potentials, but also the γ-ray strength function of 93Tc can be investigated. In addition, high-resolution in-beam γ-ray spectroscopy enables the determination of new precise nuclear structure data for 93Tc. Method: Total and partial cross-section values were measured by using the in-beam method. Prompt γ rays emitted during the irradiation of 92Mo with protons at seven different energies between 3.7 and 5.3 MeV were detected by using the high-purity germanium (HPGe) detector array HORUS at the Institute for Nuclear Physics, University of Cologne. The γγ-coincidence method was applied to correlate γ-ray cascades in 93Tc with their origin in the 92Mo+p compound state. Results: The measured cross sections are compared to Hauser-Feshbach calculations by using the statistical-model code talys on the basis of different nuclear physics input models. Using default settings based on standard phenomenological models, the experimental values cannot be reproduced. A shell-model calculation was carried out to predict the low-energy M1 strength in 93Tc. Together with Gogny-Hartree-Fock-Bogoliubov (Gogny-HFB) or Skyrme-HFB plus quasi-particle random-phase approximation (QRPA) models for the γ-ray strength function, the agreement between experimental data and theoretical predictions could be significantly improved. In addition, deviations from the adopted level scheme were found. Conclusions: By using Gogny- or Skyrme-HFB+QRPA E1 and shell-model M1 strength functions, statistical-model predictions can be significantly improved. Partial cross sections provide a valuable testing ground for γ-ray strength functions for nuclear astrophysics applications. In addition, they can be used to investigate nuclear-structure properties of the compound nucleus. [ABSTRACT FROM AUTHOR]

Extending our earlier work, a new family of three Hartree-Fock-Bogoliubov (HFB) mass models, labeled HFB-30, HFB-31, and HFB-32, is presented, along with their underlying interactions, BSk30, BSk31, and BSk32, respectively. The principle new feature is a purely phenomenological pairing term that depends on the density gradient. This enables us to have a bulk pairing term that is fitted to realistic nuclear-matter calculations in which for the first time the self-energy corrections are included, while the behavior of the nucleon effective masses in asymmetric homogeneous nuclear matter is significantly improved. Furthermore, in the particle-hole channel all the highly realistic constraints of our earlier work are retained. In particular, the unconventional Skyrme forces containing t4 and t5 terms are still constrained to fit realistic equations of state of neutron matter stiff enough to support the massive neutron stars PSR J1614-2230 and PSR J0348+0432. All unphysical long-wavelength spin and spin-isospin instabilities of nuclear matter, including the unphysical transition to a polarized state in neutron-star matter, are eliminated. Our three interactions are characterized by values of the symmetry coefficient J of 30, 31, and 32 MeV, respectively. The best fit to the database of 2353 nuclear masses is found for model HFB-31 (J=31MeV) with a model error of 0.561 MeV. This model also fits the charge-radius data with an root-mean-square error of 0.027 fm. [ABSTRACT FROM AUTHOR]

The pygmy dipole resonance and photon strength function in stable and unstable Ni and Sn isotopes are calculated within the microscopic self-consistent version of the extended theory of finite Fermi systems, which, in addition to the standard quasiparticle random-phase approximation approach, includes phonon coupling effects. The Skyrme force SLy4 is used. A pygmy dipole resonance in 72Ni is predicted at the mean energy of 12.4 MeV exhausting 25.7% of the total energy-weighted sum rule. The microscopically obtained photon El strength functions are compared with available experimental data and used to calculate nuclear reaction properties. Average radiative widths and radiative neutron capture cross sections have been calculated taking phonon coupling into account as well as uncertainties caused by various microscopic level density models. In all three quantities considered, the contribution of phonon coupling turned out to be significant and is found necessary to explain available experimental data. [ABSTRACT FROM AUTHOR]

The charge-exchange excitations in nuclei are studied within the fully self-consistent proton-neutron quasiparticle random-phase approximation using the finite-range Gogny interaction. No additional parameters beyond those included in the effective nuclear force are included. Axially symmetric deformations are consistently taken into account, both in the description of the ground-states and spin-isospin excitations. We focus on the isobaric analog and Gamow-Teller resonances. A comparison of the predicted strength distributions to the existing experimental data is presented and the role of nuclear deformation analyzed. The Gamow-Teller strength is used to estimate the ß -decay half-life of nuclei for which experimental data exist. A satisfactory agreement with experimental half-lives is found and justifies the additional study of the exotic neutron-rich N = 82, 126, and 184 isotonic chains of relevance for the r-process nucleosynthesis. [ABSTRACT FROM AUTHOR]

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 nonequipartition of parities which are known to have a significant impact on cross section predictions at low energies. Our previous global model [S. Goriely, S. Hilaire, and A. J. Koning, Phys. Rev. C 78, 064307 (2008)] suffered from deficiencies, in particular in the way the collective effects--both vibrational and rotational--were treated. We have recently improved the level density calculations using simultaneously the single-particle levels and collective properties predicted by a newly derived Gogny interaction [S. Goriely, S. Hilaire, M. Girod, and S. Péru, Phys. Rev. Lett. 102, 242501 (2009)], therefore enabling a microscopic description of energy-dependent shell, pairing, and deformation 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 reasonable results with respect to available experimental data. [ABSTRACT FROM AUTHOR]

Using quasimonochromatic laser-Compton scattering γ rays, total photoneutron cross sections were measured for 206,207,208Pb near neutron threshold with a high-efficiency 4π neutron detector. Partial E1 and M1 photoneutron cross sections along with total cross sections were determined for 207,258Pb at four energies near threshold by measuring anisotropies in photoneutron emission with linearly polarized γ rays. The E1 strength dominates over the M1 strength in the neutron channel where E1 photoneutron cross sections show extra strength of the pygmy dipole resonance in 257,208pb near the neutron threshold corresponding to 0.32%-0.42% of the Thomas-Reiche-Kuhn sum rule. Several μN² units of B(M1) ↑ strength were observed in 257,208Pb just above neutron threshold, which correspond to an M1 cross section less than 10% of the total photoneutron cross section. [ABSTRACT FROM AUTHOR]

The equation of state and composition of the inner crust of neutron stars at zero temperature are calculated, using the T = 0 version of the temperature-dependent extended Thomas-Fermi plus Strutinsky integral method, for each of a family of three functionals based on Skyrme-type forces BSkl9, BSk20, and BSk21, which are characterized by different degrees of symmetry-energy stiffness, and also for the SLy4 functional. We also solve the Tolman-Oppenheimer-Völkoff equations to calculate the distribution of mass within the inner crust. Qualitatively similar results are found for all four functionals, and in particular the number of protons per Wigner-Seitz cell is in all cases equal to 40 throughout the inner crust. [ABSTRACT FROM AUTHOR]

Masses adjacent to the classical waiting-point nuclide 130Cd have been measured by using the Penning-trap spectrometer ISOLTRAP at ISOLDE/CERN. We find a significant deviation of over 400 keV from earlier values evaluated by using nuclear beta-decay data. The new measurements show the reduction of the N = 82 shell gap below the doubly magic 132Sn. The nucleosynthesis associated with the ejected wind from type-II supemovae as well as from compact object binary mergers is studied, by using state-of-the-art hydrodynamic simulations. We find a consistent and direct impact of the newly measured masses on the calculated abundances in the A = 128-132 region and a reduction of the uncertainties from the precision mass input data. [ABSTRACT FROM AUTHOR]

Photoneutron cross sections were measured for five stable Nd isotopes, 143,144,145,146,148Nd, near neutron threshold with highly monochromatic laser-Compton scattering γ rays. The photoneutron data were compared with the calculations performed with the talys reaction code with inputs of the Skyrme Hartree-Fock-Bogoliubov (HFB) plus quasi-particle random phase approximation (QRPA) model and the axially symmetric deformed Gogny HFB plus QRPA model of E1 γ-ray strength. Using the γ-ray strength function constrained by the present photoneutron data, a thorough analysis of the reverse (n,?) cross sections is made. Radiative neutron capture cross sections for an s-process branching-point nucleus in the rare earth region, 147Nd with the half-life 10.98 d, are deduced with the ?-ray strength function method. The impact of the newly evaluated 147Nd(n,γ)148Nd cross section on s-process nucleosynthesis is discussed. [ABSTRACT FROM AUTHOR]

The TETFSI (temperature-dependent extended Thomas-Fermi plus Strutinsky integral) method for calculating the properties of the inner crust of neutron stars is here extended in the zero-temperature limit to include proton pairing. The main effect is to smooth out the proton shell effects, although the energetically favored value of Z, the number of protons per Wigner-Seitz cell, remains at, or close to, 40. [ABSTRACT FROM AUTHOR]

Photoneutron cross sections were measured for the seven stable samarium isotopes l44,147,l48,l49,l50,l52,154Sm near the neutron threshold with quasi-monochromatic laser-Compton scattering γ rays. Our photoneutron cross sections are found to be low by 20%-37% relative to existing data. The photoneutron data are analyzed with the TALYS reaction code by considering the Skyrme Hartree-Fock-Bogoliubov (HFB) plus quasiparticle random phase approximation (QRPA) model and the axially symmetric deformed Gogny HFB plus QRPA model of the £1 γ-ray strength. Using the γ-ray strength function constrained by the present photoneutron data, we made a thorough analysis of the reverse (n,γ) cross sections including the radioactive nucleus 15lSm with a half-life of 90 yr. The radiative neutron capture cross section for l53Sm with the half-life of 1.928 d is deduced with the γ-ray strength function method. [ABSTRACT FROM AUTHOR]

The Brussels-Montreal Skyrme functionals have been successful in describing properties of both finite nuclei and infinite homogeneous nuclear matter. In their latest version, these functionals have been equipped with two extra density-dependent terms in order to reproduce simultaneously ground state properties of nuclei and infinite nuclear matter properties while avoiding at the same time the arising of ferromagnetic instabilities. In the present article, we extend our previous results of the linear response theory to include such extra terms at both zero and finite temperature in pure neutron matter. The resulting formalism is then applied to derive the neutrino mean free path. The predictions from the Brussels-Montreal Skyrme functionals are compared with ab initio methods. [ABSTRACT FROM AUTHOR]

We have carried out photodisintegration cross-section measurements on 861(r using monoenergetic photon beams ranging from the neutron separation energy, Sn = 9.86 MeV, to 13 MeV. We combine our experimental 86Kr(γ, γ')85Kr cross section with results from our recent 86Kr(γ, γ') measurement below the neutron separation energy to obtain the complete nuclear dipole response of 86Kr. The new experimental information is used to predict the neutron capture cross section of 85Kr, an important branching point nucleus on the abundance flow path during s-process nucleosynthesis. Our new and more precise 85Kr(n, γ)86Kr cross section allows us to produce more precise predictions of the 86Kr abundance from s-process models. In particular, we find that the models of the s process in asymptotic giant branch stars of mass <1.5M⊕, where the 13C neutron source burns convectively rather than radiatively, represent a possible solution for the highest 86Kr:82Kr ratios observed in meteoritic stardust SiC grains. [ABSTRACT FROM AUTHOR]

The design of generation IV nuclear reactors and the studies of new fuel cycles require knowledge of the cross sections of various nuclear reactions. Our research is focused on (n,xnγ) reactions occurring in these new reactors. The aim is to measure unknown cross sections and to reduce the uncertainty on present data for reactions and isotopes of interest for transmutation or advanced reactors. The present work studies the 235U(n, n'γ) and 235U(n, 2nγ) reactions in the fast neutron energy domain (up to 20 MeV). The experiments were performed with the Geel electron linear accelerator GELINA, which delivers a pulsed white neutron beam. The time characteristics enable measuring neutron energies with the time-of-flight (TOF) technique. The neutron induced reactions [in this case inelastic scattering and (n, 2n) reactions] are identified by on-line prompt γ spectroscopy with an experimental setup including four high-purity germanium (HPGe) detectors. A fission ionization chamber is used to monitor the incident neutron flux. The experimental setup and analysis methods are presented and the model calculations performed with the TALYS-1.2 code are discussed. [ABSTRACT FROM AUTHOR]

Modeling the composition of neutron-star crusts depends strongly on binding energies of neutron-rich nuclides near the N = 50 and N = 82 shell closures. Using a recent development of time-of-flight mass spectrometry for on-line purification of radioactive ion beams to access more exotic species, we have determined for the first time the mass of 82Zn with the ISOLTRAP setup at the ISOLDE-CERN facility. With a robust neutron-star model based on nuclear energy-density-functional theory, we solve the general relativistic Tolman-Oppenheimer-Volkoff equations and calculate the neutron-star crust composition based on the new experimental mass. The composition profile is not only altered but now constrained by experimental data deeper into the crust than before. [ABSTRACT FROM AUTHOR]

The level densities and γ-ray strength functions of 105,106,111,112Cd have been extracted from particle-γ coincidence data using the Oslo method. The level densities are in very good agreement with known levels at low excitation energy. The γ-ray strength functions display no strong enhancement for low γ energies. However, more low-energy strength is apparent for 105,106Cd than for 111,112Cd. For γ energies above ~4 MeV, there is evidence for some extra strength, similar to what has been previously observed for the Sn isotopes. The origin of this extra strength is unclear; it might be due to E1 and M1 transitions originating from neutron skin oscillations or the spin-flip resonance, respectively. [ABSTRACT FROM AUTHOR]

The equilibrium properties of the outer crust of cold nonaccreting magnetars (i.e., neutron stars endowed with very strong magnetic fields) are studied using the latest experimental atomic mass data complemented with a microscopic atomic mass model based on the Hartree-Fock-Bogoliubov method. The Landau quantization of electron motion caused by the strong magnetic field is found to have a significant impact on the composition and the equation of state of crustal matter. It is also shown that the outer crust of magnetars could be much more massive than that of ordinary neutron stars. [ABSTRACT FROM AUTHOR]

We calculate the maximum mass of neutron stars for three different equations of state (EOSs) based on generalized Skyrme functionals that are simultaneously fitted to essentially all the 2003 nuclear mass data (the rms deviation is 0.58 MeV in all three cases) and to one or other of three different equations of state of pure neutron matter, each determined by a different many-body calculation using realistic two- and three-body interactions but leading to significantly different degrees of stiffness at the high densities prevailing in neutron-star interiors. The observation of a neutron star with mass 1.97 ± 0.04 M⊙ eliminates the softest of our models (BSkl9), but does not discriminate between BSk20 and BSk21. However, nuclear-mass measurements that have been made since our models were constructed strongly favor BSk21, our stiffest functional. [ABSTRACT FROM AUTHOR]

In-source resonance ionization spectroscopy of the neutron-rich actinium isotopes 225-229Ac has been performed at the ISAC facility in TRIUMF, probing a ²D3/2→4P∘5/2 atomic transition. New data on the magnetic dipole moments and changes in mean-square charge radii δ⟨r²⟩ of 226,228,229Ac have been obtained. The comparison of the measured isotope shifts and magnetic dipole coupling constants a(4P∘5/2) of 225,227Ac with a high-resolution data set is used to identify systematic uncertainties on the deduced δ⟨r²⟩A,215 and magnetic dipole moment values. The charge radii odd-even staggering is evaluated for the odd-N isotopes, showing that 226Ac has an inverted odd-even staggering that might be linked with a reflection-asymmetric shape. Comparison of the magnetic dipole moments of 225,227,229Ac with Nilsson-model estimates supports the assumption of octupole deformation in isotopes 225,227Ac and its gradual decrease toward isotope 229Ac. The changes in mean-square charge radii are compared to self-consistent calculations employing multiple modern energy density functionals: SLy5s1, BSk31, and DD-MEB1. For SLy5s1 in particular, self-consistent time-reversal breaking calculations of odd-odd nuclei incorporating finite octupole deformation are reported for the first time. For these calculations, the overall best agreement is obtained when the octupole degree of freedom is taken into account. [ABSTRACT FROM AUTHOR]

Photoneutron cross sections were measured for 137Ba and 138Ba at energies below two-neutron threshold using quasimonochromatic γ-ray beams produced in laser Compton scattering at the NewSUBARU synchrotron radiation facility. The photoneutron data are used to constrain the γ-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 γ-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. [ABSTRACT FROM AUTHOR]

The photodisintegration cross sections for the 94Mo(γ,n) and 90Zr(γ,n) reactions have been experimentally investigated with quasi-monochromatic photon beams at the High Intensity γ-ray Source (HIγS) facility of the Triangle Universities Nuclear Laboratory (TUNL). The energy dependence of the photoneutron reaction cross sections was measured with high precision from the respective neutron emission thresholds up to 13.5 MeV. These measurements contribute to a broader investigation of nuclear reactions relevant to the understanding of the p-process nucleosynthesis. The results are compared with the predictions of Hauser-Feshbach statistical model calculations using two different models for the dipole γ-ray strength function. The resulting 94Mo(γ,n) and 90Zr(γ,n) photoneutron stellar reaction rates as a function of temperature in the typical range of interest for the p-process nucleosynthesis show how sensitive the photoneutron stellar reaction rate can be to the experimental data in the vicinity of the neutron threshold. [ABSTRACT FROM AUTHOR]

Photoneutron cross sections were measured for 203Tl and 205Tl at energies between the one- and two-neutron thresholds using quasimonochromatic γ-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 γ-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 γ-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 204Tl in the context of the 205Pb-205Tl chronometry. [ABSTRACT FROM AUTHOR]

Photoneutron cross sections were measured for 58Ni,60Ni,61Ni, and 64Ni 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 63Ni, 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]