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Adsley, P. ; Hammache, F. ; de Sereville, N. ; 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 ; Wirth, H-F

• Tipo de documento: Artigo Científico
• Fonte: PHYSICAL REVIEW C; v. 103, n. 3, p. 13-pg., 2021-03-08.

Resumo

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. (AU)

• Processo FAPESP: 14/14432-2 - Investigação espectroscópica de núcleos de interesse para astrofísica nuclear
• Beneficiário: Valdir Guimarães
• Modalidade de apoio: Bolsas no Exterior - Pesquisa
• Processo FAPESP: 16/50315-6 - Experimental study of nuclear reactions of astrophysical interest
• Beneficiário: Valdir Guimarães
• Modalidade de apoio: Auxílio à Pesquisa - Regular