G. Martínez-Pinedo

Technical University Darmstadt, Darmstadt, Hesse, Germany

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Publications (241)735.66 Total impact

  • Brian Metzger, A. Arcones, E. Quataert, G. Martinez-Pinedo
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    ABSTRACT: One of the most important discoveries made with Swift is that long and short-duration gamma-ray bursts (GRBs) originate from distinct stellar progenitors. While long GRBs track ongoing star formation and result from the deaths of massive stars, short GRBs have been localized to both early and late-type galaxies, suggesting a more evolved progenitor population. Although the origin of short GRBs remains a mystery, the most popular and well-studied model is accretion following the merger of neutron star binaries. This model is qualitatively consistent with both the demographics of short GRBs and the lack of a bright associated supernova in some cases. Despite these successes, this picture has grown complex with the discovery that short GRBs are often followed by a "tail" of emission (usually soft X-rays) lasting 100 seconds after the burst. Such energetic, late-time emission from the central engine is difficult to explain in standard merger pictures. One proposed explanation is late-time "fall-back" onto the black hole of material that was ejected during the merger into highly eccentric, marginally-bound orbits. As this matter decompresses from nuclear densities, however, it undergoes rapid-neutron capture (r-process) nucleosynthesis, which can release energy comparable to the orbital binding energy. This implies that the r-process (normally thought unimportant dynamically in astrophysical contexts) has important implications for the quantity and time-dependence of fall-back and, ultimately, the source of flaring and identity of the central engine.
    01/2010;
  • 01/2010;
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    01/2010;
  • K. Sieja, G. Martínez-Pinedo, L. Coquard, N. Pietralla
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    ABSTRACT: Large scale shell-model calculations with an effective interaction derived from the realistic G-matrices were performed for N=80 isotones for which so-called mixed-symmetry states were recently observed experimentally. Calculated spectra are shown to be in good agreement with data. The calculated transition rates reveal the necessity of modifying the strength of the pairing interaction. The structure of mixed-symmetry 2+ states is analyzed in terms of seniority components and by decomposition into the Q-phonon scheme.
    Physical Review C 11/2009; 80(5). · 3.72 Impact Factor
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    ABSTRACT: Neutron-induced reaction rates, including fission, are calculated in the temperature range 1.d8 <T (K) < 1.d10 within the framework of the statistical model for targets with atomic number 83 < Z < 119 (from Po to Uuo) from the neutron to the proton drip-line. Four sets of rates have been calculated, utilizing - where possible - consistent nuclear data for neutron separation energies and fission barriers from Thomas-Fermi (TF), Extended Thomas-Fermi plus Strutinsky Integral (ETFSI), Finite-Range Droplet Model (FRDM) and Hartree-Fock-Bogolyubov (HFB) predictions. Tables of calculated values as well as analytic seven parameter fits in the standard REACLIB format are supplied. We also discuss the sensitivity of the rates to the input, aiming at a better understanding of the uncertainties introduced by the nuclear input. Comment: 14 pages, 10 figures, 2 tables in paper, 2 in Annex and online tables examples
    Astronomy and Astrophysics 11/2009; · 5.08 Impact Factor
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    ABSTRACT: We propose a new method to calculate stellar weak-interaction rates. It is based on the Thermo-Field-Dynamics formalism and allows the calculation of the weak-interaction response of nuclei at finite temperatures. The thermal evolution of the GT$_+$ distributions is presented for the sample nuclei $^{54, 56}$Fe and ~$^{76,78,80}$Ge. For Ge we also calculate the strength distribution of first-forbidden transitions. We show that thermal effects shift the GT$_+$ centroid to lower excitation energies and make possible negative- and low-energy transitions. In our model we demonstrate that the unblocking effect for GT$_+$ transitions in neutron-rich nuclei is sensitive to increasing temperature. The results are used to calculate electron capture rates and are compared to those obtained from the shell model. Comment: 16 pages, 9 figures
    Physical Review C 11/2009; · 3.72 Impact Factor
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    Almudena Arcones, Gabriel Martinez-Pinedo
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    ABSTRACT: We have performed hydrodynamical simulations of the long-time evolution of proto-neutron stars to study the nucleosynthesis using the resulting wind trajectories. Although the conditions found in the present wind models are not favourable for the production of heavy elements, a small enhancement of the entropy results in the production of r-process elements with A $\approx$ 195. This allows us to explore the sensitivity of their production to the hydrodynamical evolution (wind termination shock) and nuclear physics input used. Comment: Conference proceedings: Nuclear Physics in Astrophysics IV
    Journal of Physics Conference Series 09/2009;
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    ABSTRACT: Electron captures on nuclei play an important role in the dynamics of the collapsing core of a massive star that leads to a supernova explosion. Recent calculations of these capture rates were based on microscopic models which account for relevant degrees of freedom. Due to computational restrictions such calculations were limited to a modest number of nuclei, mainly in the mass range A=45–110. Recent supernova simulations show that this pool of nuclei, however, omits the very neutron-rich and heavy nuclei which dominate the nuclear composition during the last phase of the collapse before neutrino trapping. Assuming that the composition is given by Nuclear Statistical Equilibrium we present here electron capture rates for collapse conditions derived from individual rates for roughly 2700 individual nuclei. For those nuclei which dominate in the early stage of the collapse, the individual rates are derived within the framework of microscopic models, while for the nuclei which dominate at high densities we have derived the rates based on the Random Phase Approximation with a global parametrization of the single particle occupation numbers. In addition, we have improved previous rate evaluations by properly including screening corrections to the reaction rates into account.
    Nuclear Physics A 09/2009; · 2.50 Impact Factor
  • K. Sieja, F. Nowacki, K. Langanke, G. Martínez-Pinedo
    Physical Review C. 07/2009; 80(1).
  • K. Sieja, F. Nowacki, K. Langanke, G. Martínez-Pinedo
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    ABSTRACT: We calculate the low-lying spectra and several high-spin states of zirconium isotopes (Z=40) with neutron numbers from N=50 to N=58 using a large valence space with the 78Ni inert core, which a priori allows one to study the interplay between spherical and deformed configurations, necessary for the description of nuclides in this part of the nuclear chart. The effective interaction is derived by monopole corrections of the realistic G matrix. We reproduce essential nuclear properties, such as subshell closures in 96Zr and 98Zr. The spherical-to-deformed shape transition in 100Zr is addressed as well.
    Physical Review C 06/2009; 79(6). · 3.72 Impact Factor
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    ABSTRACT: The γ-ray decay of isomeric states in the even-even nucleus 128Cd has been observed. The nucleus of interest was produced both by the fragmentation of 136Xe and the fission of 238U primary beams. The level scheme was unambiguously constructed based on γγ coincidence relations in conjunction with detailed lifetime analysis employed for the first time on this nucleus. Large-scale shell-model calculations, without consideration of excitations across the N=82 shell closure, were performed and provide a consistent description of the experimental level scheme. The structure of the isomeric states and their decays exhibit coexistence of proton, neutron, and strongly mixed configurations due to πν interaction in overlapping orbitals for both proton and neutron holes.
    Physical Review C 05/2009; 79(1):011301(R). · 3.72 Impact Factor
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    ABSTRACT: We have computed dipole strength distributions for nickel and tin isotopes within the Relativistic Quasiparticle Time Blocking Approximation (RQTBA). These calculations provide a good description of data, including the neutron-rich tin isotopes 130,132Sn. The resulting dipole strengths have been implemented in Hauser–Feshbach calculations of astrophysical neutron capture rates relevant for r-process nucleosynthesis studies. The RQTBA calculations show the presence of enhanced dipole strength at energies around the neutron threshold for neutron rich nuclei. The computed neutron capture rates are sensitive to the fine structure of the low lying dipole strength, which emphasizes the importance of a reliable knowledge of this excitation mode.
    Nuclear Physics A 03/2009; · 2.50 Impact Factor
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    ABSTRACT: Coincidences between charged particles emitted in the β-decay of 11Li were observed using highly segmented detectors. The breakup channels involving three particles were studied in full kinematics allowing for the reconstruction of the excitation energy of the 11Be states participating in the decay. In particular, the contribution of a previously unobserved state at 16.3 MeV in 11Be has been identified selecting the channel. The angular correlations between the α particle and the center of mass of the 6He + n system favors spin and parity assignment of 3/2− for this state as well as for the previously known state at 18 MeV.
    Physics Letters B 01/2009; · 4.57 Impact Factor
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    ABSTRACT: With currently known input physics and computer simulations in one dimension, a self-consistent treatment of core-collapse supernovae does not yet lead to successful explosions, while two-dimensional models show some promise. Thus, there are strong indications that the delayed neutrino mechanism works combined with a multidimensional convection treatment for unstable layers (possibly with the aid of rotation, magnetic fields and/or still existent uncertainties in neutrino opacities). On the other hand, there is a need to provide correct nucleosynthesis abundances for the progressing field of galactic evolution and observations of low-metallicity stars. The innermost ejecta is directly affected by the explosion mechanism, i.e., most strongly, the yields of Fe group nuclei for which an induced piston or thermal bomb treatment will not provide the correct yields because the effect of neutrino interactions is not included. We apply parameterized variations to the neutrino-scattering cross sections in order to mimic in one dimension the possible increase of neutrino luminosities caused by uncertainties in proto-neutron star convection. Alternatively, parameterized variations are applied to the neutrino absorption cross sections on nucleons in the "gain region" to mimic the increase in neutrino energy deposition enabled by convective turnover. We find that both measures lead to similar results, causing explosions and a Ye > 0.5 in the innermost ejected layers, due to the combined effect of a short weak-interaction timescale and a negligible electron degeneracy, unveiling the proton-neutron mass difference. We include all weak interactions (electron and positron capture, β-decay, neutrino and antineutrino capture on nuclei, and neutrino and antineutrino capture on nucleons) and present first nucleosynthesis results for these innermost ejected layers to discuss how they improve predictions for Fe group nuclei. The proton-rich environment results in enhanced abundances of 45Sc, 49Ti, and 64Zn as required by chemical evolution studies and observations of low-metallicity stars, as well as appreciable production of nuclei in the mass range up to A = 80.
    The Astrophysical Journal 12/2008; 637(1):415. · 6.73 Impact Factor
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    ABSTRACT: The r-process constitutes one of the major challenges in nuclear astrophysics. Its astrophysical site has not yet been identified but there is observational evidence suggesting that at least two possible sites should contribute to the solar system abundance of r-process elements and that the r-process responsible for the production of elements heavier than Z=56 operates quite robustly producing always the same relative abundances. From the nuclear-physics point of view the r-process requires the knowledge of a large number of reaction rates involving exotic nuclei. These include neutron capture rates, beta-decays and fission rates, the latter for the heavier nuclei produced in the r-process. We have developed for the first time a complete database of reaction rates that in addition to neutron-capture rates and beta-decay half-lives includes all possible reactions that can induce fission (neutron-capture, beta-decay and spontaneous fission) and the corresponding fission yields. In addition, we have implemented these reaction rates in a fully implicit reaction network. We have performed r-process calculations for the neutrino-driven wind scenario to explore whether or not fission can contribute to provide a robust r-process pattern.
    12/2008;
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    ABSTRACT: The masses of very neutron-deficient nuclides close to the astrophysical r p- and ν p-process paths have been determined with the Penning trap facilities JYFLTRAP at JYFL/Jyväskylä and SHIPTRAP at GSI/Darmstadt. Isotopes from yttrium (Z=39) to palladium (Z=46) have been produced in heavy-ion fusion-evaporation reactions. In total, 21 nuclides were studied, and almost half of the mass values were experimentally determined for the first time: 88Tc, 90-92Ru, 92-94Rh, and 94,95Pd. For the 95Pdm, (21/2+) high-spin state, a first direct mass determination was performed. Relative mass uncertainties of typically δm/m=5×10-8 were obtained. The impact of the new mass values has been studied in ν p-process nucleosynthesis calculations. The resulting reaction flow and the final abundances are compared with those obtained with the data of the Atomic Mass Evaluation 2003.
    Physical Review C 11/2008; 78(5). · 3.72 Impact Factor
  • K. Langanke, G. Martinez-Pinedo, D. J. Dean
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    ABSTRACT: We investigate the effects of single-particle structure and pairing on the equilibration of positive and negative-parity level densities for the even-even nuclei 58,62,66Fe and 58Ni and the odd-A nuclei 59Ni and 65Fe. Calculations are performed using the shell model Monte Carlo method in the complete fp−gds shell-model space using a pairing+quadrupole type residual interaction. We find for the even-even nuclei that the positive-parity states dominate at low excitation energies due to strong pairing correlations. At excitation energies at which pairs are broken, single-particle structure of these nuclei is seen to play the decisive role for the energy dependence of the ratio of negative-to-positive parity level densities. We also find that equilibration energies are noticeably lower for the odd-A nuclei 59Ni and 65Fe than for the neighboring even-even nuclei 58Ni and 66Fe.
    AIP Conference Proceedings. 11/2008; 1072(1).
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    C. Barbieri, E. Caurier, K. Langanke, G. Martínez-Pinedo
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    ABSTRACT: We respond to a Comment on our recent paper (Phys.Rev.C77:024304,2008) by Paar (arXiv:0803.0274).
    Physical Review C 10/2008; · 3.72 Impact Factor
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    ABSTRACT: Systematic mean-field calculations of the β-decay rates for the nuclei with charge numbers Z=42–49 approaching the possible r-process paths in vicinity of the spherical neutron shell at N=82 are performed within the DF+CQRPA framework employing a self-consistent approach to the nuclear ground states based on the local energy-density functional (DF) theory. The calculated ground state properties are compared with the available experimental data. The beta-strength-functions of the Gamow–Teller and first-forbidden decays and the total β-decay half-lives are calculated within the continuum QRPA approach. If available, data and half-lives obtained on the basis of the Finite Range Droplet Model and the shell model are compared to our results. The effects of our calculated half-lives on the r-process abundances are explored in local r-process calculations.
    Nuclear Physics A 09/2008; · 2.50 Impact Factor
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    ABSTRACT: Baryonic outflows from proto-neutron stars formed in core-collapse supernova explosions are one of the possible scenarios for the production of heavy elements via the r-process. If the ejected mat-ter reaches supersonic velocities the outflow is known as neutrino-driven wind. We have studied the long-time evolution of proto-neutron stars with one-and two-dimensional hydrodynamical simulations and performed nucleosynthesis calculations with the resulting wind trajectories. We find that the present wind models are much closer than previous studies to provide suitable con-ditions for r-process nucleosynthesis. Moreover, we explored the effect of the wind terminations shock, nuclear physics input, and composition of the outer layers of the neutron star on the nucle-osynthesis production.
    09/2008;

Publication Stats

4k Citations
735.66 Total Impact Points

Institutions

  • 2007–2014
    • Technical University Darmstadt
      • Institute of Nuclear Physics
      Darmstadt, Hesse, Germany
    • GSI Helmholtzzentrum für Schwerionenforschung
      • ExtreMe Matter Institute EMMI and Research Division
      Darmstadt, Hesse, Germany
  • 2004–2008
    • Autonomous University of Barcelona
      Cerdanyola del Vallès, Catalonia, Spain
    • University of Münster
      Muenster, North Rhine-Westphalia, Germany
  • 2000–2008
    • Universität Basel
      • Department of Physics
      Basel, BS, Switzerland
  • 1998–2007
    • Aarhus University
      • Department of Physics and Astronomy
      Aars, Region North Jutland, Denmark
  • 1993–2007
    • Universidad Autónoma de Madrid
      • Departamento de Física Teórica
      Madrid, Madrid, Spain
  • 2003–2006
    • IEEC Institute of Space Studies of Catalonia
      Barcino, Catalonia, Spain
    • University of Tennessee
      • Department of Physics & Astronomy
      Knoxville, TN, United States
  • 2003–2004
    • Catalan Institution for Research and Advanced Studies
      Barcino, Catalonia, Spain
  • 2001
    • University of California, Santa Cruz
      • Department of Astronomy and Astrophysics
      Santa Cruz, CA, United States
  • 1998–1999
    • California Institute of Technology
      • Department of Physics
      Pasadena, CA, United States