β+ Gamow-teller transition strengths from Ti 46 and stellar electron-capture rates

S. Noji, R. G.T. Zegers, Sam M. Austin, T. Baugher, D. Bazin, B. A. Brown, C. M. Campbell, A. L. Cole, H. J. Doster, A. Gade, C. J. Guess, S. Gupta, G. W. Hitt, C. Langer, S. Lipschutz, E. Lunderberg, R. Meharchand, Z. Meisel, G. Perdikakis, J. PereiraF. Recchia, H. Schatz, M. Scott, S. R. Stroberg, C. Sullivan, L. Valdez, C. Walz, D. Weisshaar, S. J. Williams, K. Wimmer

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Abstract

The Gamow-Teller strength in the β+ direction to Sc46 was extracted via the Ti46(t,He3+γ) reaction at 115MeV/u. The γ-ray coincidences served to precisely measure the very weak Gamow-Teller transition to a final state at 991 keV. Although this transition is weak, it is crucial for accurately estimating electron-capture rates in astrophysical scenarios with relatively low stellar densities and temperatures, such as presupernova stellar evolution. Shell-model calculations with different effective interactions in the pf shell-model space do not reproduce the experimental Gamow-Teller strengths, which is likely due to sd-shell admixtures. Calculations in the quasiparticle random phase approximation that are often used in astrophysical simulations also fail to reproduce the experimental Gamow-Teller strength distribution, leading to strongly overestimated electron-capture rates. Because reliable theoretical predictions of Gamow-Teller strengths are important for providing astrophysical electron-capture reaction rates for a broad set of nuclei in the lower pf shell, we conclude that further theoretical improvements are required to match astrophysical needs.

Original languageEnglish
Article number252501
JournalPhysical Review Letters
Volume112
Issue number25
DOIs
StatePublished - Jun 25 2014

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