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Title: The role of fission on neutron star mergers and its impact on the r-process peaks

Abstract

The comparison between observational abundance features and those obtained from nucleosynthesis predictions of stellar evolution and/or explosion simulations can scrutinize two aspects: (a) the conditions in the astrophysical production site and (b) the quality of the nuclear physics input utilized. Here we test the abundance features of r-process nucleosynthesis calculations using four different fission fragment distribution models. Furthermore, we explore the origin of a shift in the third r-process peak position in comparison with the solar r-process abundances which has been noticed in a number of merger nucleosynthesis predictions. We show that this shift occurs during the r-process freeze-out when neutron captures and β-decays compete and an (n,γ)-(γ,n) equilibrium is not maintained anymore. During this phase neutrons originate mainly from fission of material above A = 240. We also investigate the role of β-decay half-lives from recent theoretical advances, which lead either to a smaller amount of fissioning nuclei during freeze-out or a faster (and thus earlier) release of fission neutrons, which can (partially) prevent this shift and has an impact on the second and rare-earth peak as well.

Authors:
;  [1]; ; ;  [2];  [3];  [4]; ;  [5];  [6];  [7];  [8];  [9];  [8];  [10];  [11]
  1. Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4055 Basel (Switzerland)
  2. Institut für Kernphysik, Technische Universität Darmstadt, Schlossgartenstrasse 2, D-64289 Darmstadt (Germany)
  3. (Germany)
  4. GSI Helmholtzzentrum fr Schwerionenforschung GmbH, Planckstrasse 1, D-64291 Darmstadt (Germany)
  5. The Oskar Klein Centre, Department of Astronomy, AlbaNova, Stockholm University, SE-10691 Stockholm (Sweden)
  6. Department of Physics, Faculty of Science, University of Zagreb, 10000 Zagreb (Croatia)
  7. SSC RF ITEP of NRC “Kurchatov Institute”, Bolshaya Cheremushkinskaya 25, 117218 Moscow (Russian Federation)
  8. (Switzerland)
  9. Centre for Astrophysics Research, School of Physics, Astronomy and Mathematics, University of Hertfordshire, Hatfield AL10 9AB (United Kingdom)
  10. Institut Energie am Bau, Fachhochschule Nordwestschweiz, St. Jakobs-Strasse 84, 4132 Muttenz (Switzerland)
  11. Department of Physics and Astronomy, Aarhus University, Ny Munkegade, bygn. 1520, DK-8000 Aarhus C (Denmark)
Publication Date:
OSTI Identifier:
22609082
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Conference Proceedings; Journal Volume: 1743; Journal Issue: 1; Conference: CETUP 2015: Workshop on dark matter, neutrino physics and astrophysics, Deadwood, SD (United States), 15 Jun - 17 Jul 2015, PPC 2015: 9. international conference on interconnections between particle physics and cosmology, Deadwood, SD (United States), 15 Jun - 17 Jul 2015; Other Information: (c) 2016 Author(s); Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS; 79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ASTROPHYSICS; BETA DECAY; CAPTURE; DISTRIBUTION; EQUILIBRIUM; EXPLOSIONS; FISSION; FISSION FRAGMENTS; FORECASTING; HALF-LIFE; NEUTRON REACTIONS; NEUTRON STARS; NUCLEAR PHYSICS; NUCLEI; NUCLEOSYNTHESIS; R PROCESS; SIMULATION

Citation Formats

Eichler, M., E-mail: marius.eichler@unibas.ch, Thielemann, F.-K., Arcones, A., Langanke, K., Martinez-Pinedo, G., GSI Helmholtzzentrum fr Schwerionenforschung GmbH, Planckstrasse 1, D-64291 Darmstadt, Kelic, A., Korobkin, O., Rosswog, S., Marketin, T., Panov, I., Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4055 Basel, Rauscher, T., Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4055 Basel, Winteler, C., and Zinner, N. T.. The role of fission on neutron star mergers and its impact on the r-process peaks. United States: N. p., 2016. Web. doi:10.1063/1.4953296.
Eichler, M., E-mail: marius.eichler@unibas.ch, Thielemann, F.-K., Arcones, A., Langanke, K., Martinez-Pinedo, G., GSI Helmholtzzentrum fr Schwerionenforschung GmbH, Planckstrasse 1, D-64291 Darmstadt, Kelic, A., Korobkin, O., Rosswog, S., Marketin, T., Panov, I., Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4055 Basel, Rauscher, T., Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4055 Basel, Winteler, C., & Zinner, N. T.. The role of fission on neutron star mergers and its impact on the r-process peaks. United States. doi:10.1063/1.4953296.
Eichler, M., E-mail: marius.eichler@unibas.ch, Thielemann, F.-K., Arcones, A., Langanke, K., Martinez-Pinedo, G., GSI Helmholtzzentrum fr Schwerionenforschung GmbH, Planckstrasse 1, D-64291 Darmstadt, Kelic, A., Korobkin, O., Rosswog, S., Marketin, T., Panov, I., Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4055 Basel, Rauscher, T., Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4055 Basel, Winteler, C., and Zinner, N. T.. Tue . "The role of fission on neutron star mergers and its impact on the r-process peaks". United States. doi:10.1063/1.4953296.
@article{osti_22609082,
title = {The role of fission on neutron star mergers and its impact on the r-process peaks},
author = {Eichler, M., E-mail: marius.eichler@unibas.ch and Thielemann, F.-K. and Arcones, A. and Langanke, K. and Martinez-Pinedo, G. and GSI Helmholtzzentrum fr Schwerionenforschung GmbH, Planckstrasse 1, D-64291 Darmstadt and Kelic, A. and Korobkin, O. and Rosswog, S. and Marketin, T. and Panov, I. and Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4055 Basel and Rauscher, T. and Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4055 Basel and Winteler, C. and Zinner, N. T.},
abstractNote = {The comparison between observational abundance features and those obtained from nucleosynthesis predictions of stellar evolution and/or explosion simulations can scrutinize two aspects: (a) the conditions in the astrophysical production site and (b) the quality of the nuclear physics input utilized. Here we test the abundance features of r-process nucleosynthesis calculations using four different fission fragment distribution models. Furthermore, we explore the origin of a shift in the third r-process peak position in comparison with the solar r-process abundances which has been noticed in a number of merger nucleosynthesis predictions. We show that this shift occurs during the r-process freeze-out when neutron captures and β-decays compete and an (n,γ)-(γ,n) equilibrium is not maintained anymore. During this phase neutrons originate mainly from fission of material above A = 240. We also investigate the role of β-decay half-lives from recent theoretical advances, which lead either to a smaller amount of fissioning nuclei during freeze-out or a faster (and thus earlier) release of fission neutrons, which can (partially) prevent this shift and has an impact on the second and rare-earth peak as well.},
doi = {10.1063/1.4953296},
journal = {AIP Conference Proceedings},
number = 1,
volume = 1743,
place = {United States},
year = {Tue Jun 21 00:00:00 EDT 2016},
month = {Tue Jun 21 00:00:00 EDT 2016}
}
  • Comparing observational abundance features with nucleosynthesis predictions of stellar evolution or explosion simulations, we can scrutinize two aspects: (a) the conditions in the astrophysical production site and (b) the quality of the nuclear physics input utilized. We test the abundance features of r-process nucleosynthesis calculations for the dynamical ejecta of neutron star merger simulations based on three different nuclear mass models: The Finite Range Droplet Model, the (quenched version of the) Extended Thomas Fermi Model with Strutinsky Integral, and the Hartree–Fock–Bogoliubov mass model. We make use of corresponding fission barrier heights and compare the impact of four different fission fragmentmore » distribution models on the final r-process abundance distribution. In particular, we explore the abundance distribution in the second r-process peak and the rare-earth sub-peak as a function of mass models and fission fragment distributions, as well as the origin of a shift in the third r-process peak position. The latter has been noticed in a number of merger nucleosynthesis predictions. We show that the shift occurs during the r-process freeze-out when neutron captures and β-decays compete and an (n,γ)–(γ,n) equilibrium is no longer maintained. During this phase neutrons originate mainly from fission of material above A = 240. We also investigate the role of β-decay half-lives from recent theoretical advances, which lead either to a smaller amount of fissioning nuclei during freeze-out or a faster (and thus earlier) release of fission neutrons, which can (partially) prevent this shift and has an impact on the second and rare-earth peak as well.« less
  • Here, when binary systems of neutron stars merge, a very small fraction of their rest mass is ejected, either dynamically or secularly. This material is neutron-rich and its nucleosynthesis provides the astrophysical site for the production of heavy elements in the Universe, together with a kilonova signal confirming neutron-star mergers as the origin of short gamma-ray bursts. We perform full general-relativistic simulations of binary neutron-star mergers employing three different nuclear-physics equations of state (EOSs), considering both equal- and unequal-mass configurations, and adopting a leakage scheme to account for neutrino radiative losses. Using a combination of techniques, we carry out anmore » extensive and systematic study of the hydrodynamical, thermodynamical, and geometrical properties of the matter ejected dynamically, employing the WinNet nuclear-reaction network to recover the relative abundances of heavy elements produced by each configurations. Among the results obtained, three are particularly important. First, we find that, within the sample considered here, both the properties of the dynamical ejecta and the nucleosynthesis yields are robust against variations of the EOS and masses. Second, using a conservative but robust criterion for unbound matter, we find that the amount of ejected mass is ≲10 –3 M⊙, hence at least one order of magnitude smaller than what normally assumed in modelling kilonova signals. Finally, using a simplified and gray-opacity model we assess the observability of the infrared kilonova emission finding, that for all binaries the luminosity peaks around ~1/2 day in the H-band, reaching a maximum magnitude of –13, and decreasing rapidly after one day.« less
    Cited by 5
  • About half of heavy elements are considered to be produced by the rapid neutron-capture process, r-process. The neutron star merger is one of the viable candidates for the astrophysical site of r-process nucleosynthesis. Nuclear fission reactions play an important role in the r-process of neutron star mergers. However theoretical predictions about fission properties of neutron-rich nuclei have some uncertainties. Especially, their fission fragment distributions are totally unknown and the phenomenologically extrapolated distribution was often applied to nucleosynthesis calculations. In this study, we have carried out r-process nucleosynthesis calculations based upon new theoretical estimates of fission fragment distributions. We discuss themore » effects on the r-process in neutron star mergers from the nuclear fission of heavy neutron-rich actinide elements. We also discuss how variations in the fission fragment distributions affect the abundance pattern.« less
  • Almost half of heavy nuclei beyond iron are considered to be produced by rapid neutron capture process (r-process). This process occurs in the neutron-rich environment such as core-collapse supernovae or neutron star mergers, but the main production site is still unknown. In the r-process of neutron star mergers, nuclear fission reactions play an important role. Also beta-decay half-lives of magic nuclei are crucial for the r-process. We have carried out r-process nucleosynthesis calculations based upon new theoretical estimates of fission fragment distributions and new beta-decay half-lives for N=82 nuclei measured at RIBF-RIKEN. We investigate the effect of nuclear fission onmore » abundance patterns in the matter ejected from neutron star mergers with two different fission fragment mass distributions. We also discuss how the new experimental beta-decay half-lives affect the r-process.« less
  • We consider hot accretion disk outflows from black hole-neutron star mergers in the context of the nucleosynthesis they produce. We begin with a three-dimensional numerical model of a black hole-neutron star merger and calculate the neutrino and antineutrino fluxes emitted from the resulting accretion disk. We then follow the element synthesis in material outflowing the disk along parameterized trajectories. We find that at least a weak r-process is produced, and in some cases a main r-process as well. The neutron-rich conditions required for this production of r-process nuclei stem directly from the interactions of the neutrinos emitted by the diskmore » with the free neutrons and protons in the outflow.« less