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Sökning: WFRF:(Kostensalo J.)

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1.
  • Kirsebom, O. S., et al. (författare)
  • Measurement of the 2+→0+ ground-state transition in the β decay of F 20
  • 2019
  • Ingår i: Physical Review C. - 2469-9985. ; 100:6
  • Tidskriftsartikel (refereegranskat)abstract
    • We report the first detection of the second-forbidden, nonunique, 2+→0+, ground-state transition in the β decay of F20. A low-energy, mass-separated F+20 beam produced at the IGISOL facility in Jyväskylä, Finland, was implanted in a thin carbon foil and the β spectrum measured using a magnetic transporter and a plastic-scintillator detector. The β-decay branching ratio inferred from the measurement is bβ=[0.41±0.08(stat)±0.07(sys)]×10-5 corresponding to logft=10.89(11), making this one of the strongest second-forbidden, nonunique β transitions ever measured. The experimental result is supported by shell-model calculations and has significant implications for the final evolution of stars that develop degenerate oxygen-neon cores. Using the new experimental data, we argue that the astrophysical electron-capture rate on Ne20 is now known to within better than 25% at the relevant temperatures and densities.
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2.
  • Kirsebom, O. S., et al. (författare)
  • Discovery of an Exceptionally Strong β -Decay Transition of F 20 and Implications for the Fate of Intermediate-Mass Stars
  • 2019
  • Ingår i: Physical Review Letters. - 0031-9007. ; 123:26
  • Tidskriftsartikel (refereegranskat)abstract
    • A significant fraction of stars between 7 and 11 solar masses are thought to become supernovae, but the explosion mechanism is unclear. The answer depends critically on the rate of electron capture on Ne20 in the degenerate oxygen-neon stellar core. However, because of the unknown strength of the transition between the ground states of Ne20 and F20, it has not previously been possible to fully constrain the rate. By measuring the transition, we establish that its strength is exceptionally large and that it enhances the capture rate by several orders of magnitude. This has a decisive impact on the evolution of the core, increasing the likelihood that the star is (partially) disrupted by a thermonuclear explosion rather than collapsing to form a neutron star. Importantly, our measurement resolves the last remaining nuclear physics uncertainty in the final evolution of degenerate oxygen-neon stellar cores, allowing future studies to address the critical role of convection, which at present is poorly understood
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