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

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

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

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

URI: http://localhost:8080/xmlui/handle/123456789/550

Date: 2016-11-22

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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