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- Kirsebom, O. S., et al.
(författare)
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Discovery of an Exceptionally Strong β -Decay Transition of F 20 and Implications for the Fate of Intermediate-Mass Stars
- 2019
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Ingår i: Physical Review Letters. - 0031-9007. ; 123:26
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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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| 2. |
- Kirsebom, O. S., et al.
(författare)
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Measurement of the 2+→0+ ground-state transition in the β decay of F 20
- 2019
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Ingår i: Physical Review C. - 2469-9985. ; 100:6
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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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| 6. |
- IDS Collaboration, HASH(0x3dac240), et al.
(författare)
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Beta-delayed proton emission from 20Mg
- 2016
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Ingår i: European Physical Journal A. - : Springer Science and Business Media LLC. - 1434-601X .- 1434-6001. ; 52:10, s. 304-
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Tidskriftsartikel (refereegranskat)abstract
- Beta-delayed proton emission from 20 Mg has been measured at ISOLDE, CERN, with the ISOLDE Decay Station (IDS) setup including both charged-particle and gamma-ray detection capabilities. A total of 27 delayed proton branches were measured including seven so far unobserved. An updated decay scheme, including three new resonances above the proton separation energy in 20 Na and more precise resonance energies, is presented. Beta-decay feeding to two resonances above the Isobaric Analogue State (IAS) in 20 Na is observed. This may allow studies of the 4032.9(2.4)keV resonance in 19 Ne through the beta decay of 20 Mg, which is important for the astrophysically relevant reaction 15O(?,?)19Ne. Beta-delayed protons were used to obtain a more precise value for the half-life of 20 Mg, 91.4(1.0)ms.
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| 8. |
- Kirsebom, O. S., et al.
(författare)
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First Accurate Normalization of the β -delayed α Decay of N 16 and Implications for the C 12 (α,γ) O 16 Astrophysical Reaction Rate
- 2018
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Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 121:14
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Tidskriftsartikel (refereegranskat)abstract
- Published by the American Physical Society. The C12(α,γ)O16 reaction plays a central role in astrophysics, but its cross section at energies relevant for astrophysical applications is only poorly constrained by laboratory data. The reduced α width, γ11, of the bound 1- level in O16 is particularly important to determine the cross section. The magnitude of γ11 is determined via sub-Coulomb α-transfer reactions or the β-delayed α decay of N16, but the latter approach is presently hampered by the lack of sufficiently precise data on the β-decay branching ratios. Here we report improved branching ratios for the bound 1- level [bβ,11=(5.02±0.10)×10-2] and for β-delayed α emission [bβα=(1.59±0.06)×10-5]. Our value for bβα is 33% larger than previously held, leading to a substantial increase in γ11. Our revised value for γ11 is in good agreement with the value obtained in α-transfer studies and the weighted average of the two gives a robust and precise determination of γ11, which provides significantly improved constraints on the C12(α,γ) cross section in the energy range relevant to hydrostatic He burning.
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| 10. |
- Mao, Guanzhong, et al.
(författare)
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Cleavage of Model Substrates by Arabidopsis thaliana PRORP1 Reveals New Insights into Its Substrate Requirements
- 2016
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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 11:8
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Tidskriftsartikel (refereegranskat)abstract
- Two broad classes of RNase P trim the 5' leader of precursor tRNAs (pre-tRNAs): ribonucleoprotein (RNP)- and proteinaceous (PRORP)-variants. These two RNase P types, which use different scaffolds for catalysis, reflect independent evolutionary paths. While the catalytic RNA-based RNP form is present in all three domains of life, the PRORP family is restricted to eukaryotes. To obtain insights on substrate recognition by PRORPs, we examined the 5' processing ability of recombinant Arabidopsis thaliana PRORP1 (AtPRORP1) using a panel of pre-tRNA(Ser) variants and model hairpin-loop derivatives (pATSer type) that consist of the acceptor-T-stem stack and the T-/D-loop. Our data indicate the importance of the identity of N-1 (the residue immediately 5' to the cleavage site) and the N-1: N+73 base pair for cleavage rate and site selection of pre-tRNA(Ser) and pATSer. The nucleobase preferences that we observed mirror the frequency of occurrence in the complete suite of organellar pre-tRNAs in eight algae/plants that we analyzed. The importance of the T-/D-loop in pre-tRNA(Ser) for tight binding to AtPRORP1 is indicated by the 200-fold weaker binding of pATSer compared to pre-tRNA(Ser), while the essentiality of the T-loop for cleavage is reflected by the near-complete loss of activity when a GAAA-tetraloop replaced the T-loop in pATSer. Substituting the 2'-OH at N-1 with 2'-H also resulted in no detectable cleavage, hinting at the possible role of this 2'-OH in coordinating Mg2+ ions critical for catalysis. Collectively, our results indicate similarities but also key differences in substrate recognition by the bacterial RNase P RNP and AtPRORP1: while both forms exploit the acceptor-T-stem stack and the elbow region in the pre-tRNA, the RNP form appears to require more recognition determinants for cleavage-site selection.
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