期刊
PHYSICAL REVIEW C
卷 103, 期 3, 页码 -出版社
AMER PHYSICAL SOC
DOI: 10.1103/PhysRevC.103.035804
关键词
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资金
- IN2P3-ASCR LEA NuAG
- Sao Paulo Research Foundation (FAPESP) [16/50315-6, 14/14432-2]
- Deanship of Scientific Research, Jazan University
- Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP) [14/14432-2, 16/50315-6] Funding Source: FAPESP
The neutron-unbound levels in F-19 predominantly decay by alpha-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 to accurately determine the reaction rates.
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.
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