Constraints for stellar electron-capture rates on 86Kr via the 86Kr(t ,3He+γ )86Br reaction and the implications for core-collapse supernovae
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 86Kr to 86Br, 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 86Kr were extracted from the 86Kr(t ,3He+γ ) charge-exchange reaction at 115 MeV /u . The electron-capture rates were calculated as a function of stellar density and temperature. Besides the case of 86Kr, 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 86Kr 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.- Publication:
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Physical Review C
- Pub Date:
- October 2019
- DOI:
- 10.1103/PhysRevC.100.045805
- arXiv:
- arXiv:1908.03985
- Bibcode:
- 2019PhRvC.100d5805T
- Keywords:
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- Nuclear Experiment;
- Astrophysics - High Energy Astrophysical Phenomena;
- Astrophysics - Solar and Stellar Astrophysics;
- Nuclear Theory
- E-Print:
- 15 pages, 10 figures