Constraints for stellar electron-capture rates on Kr-86 via the Kr-86(t, He-3 + gamma)Br-86 reaction and the implications for core-collapse supernovae

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Titus, E. R. ; Ney, E. M. ; Zegers, R. G. T. ; Bazin, D. ; Belarge, J. ; Bender, P. C. ; Brown, B. A. ; Campbell, C. M. ; Elman, B. ; Engel, J. ; Gade, A. ; Gao, B. ; Kwan, E. ; Lipschutz, S. ; Longfellow, B. ; Lunderberg, E. ; Mijatovic, T. ; Noji, S. ; Pereira, J. ; Schmitt, J. ; Sullivan, C. ; Weisshaar, D. ; Zamora, J. C.

• Document type: Journal article
• Source: PHYSICAL REVIEW C; v. 100, n. 4, p. 14-pg., 2019-10-22.

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 Kr-86 to Br-86, 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 Kr-86 were extracted from the Kr-86(t, He-3 + gamma) charge-exchange reaction at 115MeV/u. The electron-capture rates were calculated as a function of stellar density and temperature. Besides the case of Kr-86, 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 Kr-86 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. (AU)

• FAPESP's process: 18/04965-4 - Study of structure and nuclear reactions induced by exotic nuclei using active targets
• Grantee: Juan Carlos Zamora Cardona
• Support Opportunities: Scholarships in Brazil - Post-Doctoral