β+ Gamow-Teller Transition Strengths from Ti46 and Stellar Electron-Capture Rates

S. Noji et al.
Phys. Rev. Lett. 112, 252501 – Published 25 June 2014

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.

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  • Received 5 April 2014

DOI:https://doi.org/10.1103/PhysRevLett.112.252501

© 2014 American Physical Society

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Vol. 112, Iss. 25 — 27 June 2014

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