Charged-particle branching ratios above the neutron threshold in F-19: Constraining N-15 production in core-collapse supernovae

Adsley, P.; Hammache, F.; Sereville, N. de; Alcindor, V.; Assie, M.; Beaumel, D.; Chabot, M.; Degerlier, M.; Delafosse, C.; Faestermann, T.; Flavigny, F.; Fox, S. P.; Garg, R.; Georgiadou, A.; Gillespie, S. A.; Guillot, J.; Guimaraes, V.; Gottardo, A.; Hertenberger, R.; Kiener, J.; Laird, A. M.; Lefebvre-Schuhl, A.; Matea, I.; Meyer, A.; Mahgoub, M.; Olivier, L.; Perrot, L.; Riley, J.; Sivacek, I.; Stefan, I.; Tatischeff, V. und Wirth, H.-F. (2021): Charged-particle branching ratios above the neutron threshold in F-19: Constraining N-15 production in core-collapse supernovae. In: Physical Review C, Bd. 103, Nr. 3, 35804

Abstract

Background: Spatially correlated overabundances of N-15 and O-18 observed in some low-density graphite meteoritic grains have been connected to nucleosynthesis taking place in the helium-burning shell during core-collapse supernovae. Two of the reactions which have been identified as important to the final abundances of N-15 and O-18 are F-18(n, alpha) N-15 and F-18(n, p) O-18. The relative strengths of the F-18(n, alpha) N-15 and F-18(n, p) O-18 reactions depend sensitively on the relative alpha(0) and p(0) decay branches from states above the neutron threshold in F-19 in addition to other properties such as the spins, parities, and neutron widths. However, experimental data on the charged-particle decays from these highly excited states are lacking or inconsistent. Purpose: We measure the charged-particle decay branches from states around the neutron threshold in F-19. Method: Two experiments were performed using proton inelastic scattering from LiF targets and magnetic spectrographs. The first experiment used the high-resolution Q3D spectrograph at Munich to constrain the properties of levels in F-19. A second experiment using the Orsay split-pole spectrograph and an array of silicon detectors was performed in order To measure the charged-particle decay branches from states around the neutron threshold in F-19. Results: A number of levels in F-19 have been identified along with their corresponding charged-particle decays. The first state above the neutron threshold which has an observed proton-decay branch to the ground state of O-18 lies 68 keV (E-x = 10.5 MeV) above the neutron threshold. The alpha-particle decays from the neutron-unbound levels are generally observed to be much stronger than the proton decays. Conclusion:Neutron-unbound levels in F-19 are observed to decay predominantly by a-particle emission, supporting the role of F-18(n, alpha) N-15 in the production of N-15 in the helium-burning shell of supernovae. Improved resonant-scattering reaction data are required in order to be able to determine the reaction rates accurately.

• Dokumententyp: Zeitschriftenartikel
• Fakultät: Physik
• Themengebiete: 500 Naturwissenschaften und Mathematik > 530 Physik
• ISSN: 2469-9985
• Sprache: Englisch