Constraints for stellar electron-capture rates on Kr86 via the Kr86(t,He3+γ)Br86 reaction and the implications for core-collapse supernovae

R. Titus, E. M. Ney, R. G. T. Zegers, D. Bazin, J. Belarge, P. C. Bender, B. A. Brown, C. M. Campbell, B. Elman, J. Engel, A. Gade, B. Gao, E. Kwan, S. Lipschutz, B. Longfellow, E. Lunderberg, T. Mijatović, S. Noji, J. Pereira, J. Schmitt, C. Sullivan, D. Weisshaar, and J. C. Zamora
Phys. Rev. C 100, 045805 – Published 22 October 2019

Abstract

Background: In the late stages of stellar core collapse just prior to core bounce, electron captures on medium-heavy nuclei drive deleptonization. Therefore, simulations require the use of accurate reaction rates. Nuclei with neutron number near N=50 above atomic number Z=28 play an important role. Rates presently used in astrophysical simulations rely primarily on a relatively simple single-state approximation. In order to improve the accuracy of the astrophysical simulations, experimental data are needed to test the electron-capture rates and to guide the development of better theoretical models and astrophysical simulations.

Purpose: The purpose of the present work was to measure the Gamow-Teller transition strength from Kr86 to Br86, to derive the stellar electron-capture rates based on the extracted strengths, and to compare the derived rates with rates based on shell-model and quasiparticle random-phase approximation (QRPA) Gamow-Teller strengths calculations, as well as the single-state approximation. An additional purpose was to test the impact of using improved electron-capture rates on the late evolution of core-collapse supernovae.

Method: The Gamow-Teller strengths from Kr86 were extracted from the Kr86(t,He3+γ) charge-exchange reaction at 115MeV/u. The electron-capture rates were calculated as a function of stellar density and temperature. Besides the case of Kr86, the electron-capture rates based on the QRPA calculations were calculated for 78 additional isotopes near N=50 above Z=28. The impact of using these rates instead of those based on the single-state approximation is studied in a spherically symmetrical simulation of core collapse just prior to bounce.

Results: The derived electron-capture rates on Kr86 from the experimental Gamow-Teller strength distribution are much smaller than the rates estimated based on the single-state approximation. Rates based on Gamow-Teller strengths estimated in shell-model and QRPA calculations are more accurate. The core-collapse supernova simulation with electron-capture rates based on the QRPA calculations indicate a significant reduction in the deleptonization during the collapse phase.

Conclusions: It is important to utilize microscopic theoretical models that are tested by experimental data to constrain and estimate Gamow-Teller strengths and derived electron-capture rates for nuclei near N=50 that are inputs for astrophysical simulations of core-collapse supernovae and their multimessenger signals, such as the emission of neutrinos and gravitational waves.

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  • Received 27 June 2019

DOI:https://doi.org/10.1103/PhysRevC.100.045805

©2019 American Physical Society

Physics Subject Headings (PhySH)

Nuclear Physics

Authors & Affiliations

R. Titus1,2,3, E. M. Ney4, R. G. T. Zegers1,2,3,*, D. Bazin1,3, J. Belarge1, P. C. Bender5, B. A. Brown1,2,3, C. M. Campbell6, B. Elman1,3, J. Engel4, A. Gade1,2,3, B. Gao7, E. Kwan1, S. Lipschutz1,2,3, B. Longfellow1,3, E. Lunderberg1,3, T. Mijatović1, S. Noji1,2, J. Pereira1,2, J. Schmitt1,2,3, C. Sullivan1,2,3, D. Weisshaar1, and J. C. Zamora8

  • 1National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824, USA
  • 2Joint Institute for Nuclear Astrophysics, Center for the Evolution of the Elements, Michigan State University, East Lansing, Michigan 48824, USA
  • 3Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824, USA
  • 4Department of Physics and Astronomy, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, USA
  • 5Department of Physics, University of Massachusetts Lowell, Lowell, Massachusetts 01854, USA
  • 6Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
  • 7Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, China
  • 8Instituto de Física, Universidade de São Paulo, 05508-090 São Paulo, Brazil

  • *zegers@nscl.msu.edu

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Vol. 100, Iss. 4 — October 2019

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