Background: Shell hydrogen burning during the asymptotic giant branch (AGB) phase through the oxygen isotopes has been indicated as a key process that is needed to understand the observed O-18/O-16 relative abundance in presolar grains and in stellar atmospheres. This ratio is strongly influenced by the relative strengths of the reactions O-18(p, alpha)N-15 and O-18(p, gamma)F-19 in low-mass AGB stars. While the former channel has been the focus of a large number of measurements, the (p, gamma) reaction path has only recently received some attention and its stellar reaction rate over a wide temperature range rests on only one measurement. Purpose: Our aim is the direct measurement of states in F-19 as populated through the reaction O-18(p, gamma)F-19 to better determine their influence on the astrophysical reaction rate, and more generally to improve the understanding of the nuclear structure of F-19. Method: Branchings and resonance strengths were measured in the proton energy range E-p(lab) = 150-400 keV, using a high-purity germanium detector inside a massive lead shield. The measurement took place in the ultralow-background environment of the Laboratory for Underground Nuclear Astrophysics (LUNA) experiment at the Gran Sasso National Laboratory, leading to a highly increased sensitivity. Results: The uncertainty of the gamma branchings and strengths was improved for all four resonances in the studied energy range; many new transitions were observed in the case of the 334 keV resonance, and individual gamma decays of the 215 keV resonance were measured for the first time. In addition a number of transitions to intermediate states that decay through alpha emission were identified. The strengths of the observed resonances are generally in agreement with literature values. Conclusions: Our measurements substantially confirm previous determinations of the relevant resonance strengths. Therefore the O-18(p, gamma)F-19 reaction rate does not change with respect to the reaction rate reported in the compilations commonly adopted in the extant computations of red-giant branch and AGB stellar models. Nevertheless, our measurements definitely exclude a nonstandard scenario for the fluorine nucleosynthesis and a nuclear physics solution for the O-18 depletion observed in Group 2 oxygen-rich stardust grains.

Low-energy resonances in the O-18(p, gamma)F-19 reaction [Low-energy resonances in the O 18 (p,γ)19 F reaction] / F.R. Pantaleo, A. Boeltzig, A. Best, R. Perrino, M. Aliotta, J. Balibrea-Correa, F. Barile, D. Bemmerer, C. Broggini, C.G. Bruno, R. Buompane, A. Caciolli, F. Cavanna, T. Chillery, G.F. Ciani, P. Corvisiero, L. Csedreki, T. Davinson, R.J. deBoer, R. Depalo, G. D'Erasmo, A. Di Leva, Z. Elekes, F. Ferraro, E.M. Fiore, A. Formicola, Z. Fülöp, G. Gervino, A. Guglielmetti, C. Gustavino, G. Gyürky, G. Imbriani, M. Junker, I. Kochanek, M. Lugaro, E. Masha, R. Menegazzo, V. Mossa, V. Paticchio, D. Piatti, P. Prati, D. Rapagnani, L. Schiavulli, K. Stöckel, O. Straniero, T. Szücs, M.P. Takács, D. Trezzi, M. Wiescher, S. Zavatarelli. - In: PHYSICAL REVIEW C. - ISSN 2469-9985. - 104:2(2021 Aug 11), pp. 025802.025802-1-025802.025802-12. [10.1103/PhysRevC.104.025802]

Low-energy resonances in the O-18(p, gamma)F-19 reaction [Low-energy resonances in the O 18 (p,γ)19 F reaction]

R. Depalo
Membro del Collaboration Group
;
F. Ferraro
Membro del Collaboration Group
;
A. Guglielmetti
Membro del Collaboration Group
;
E. Masha
Membro del Collaboration Group
;
D. Trezzi
Membro del Collaboration Group
;
2021-08-11

Abstract

Background: Shell hydrogen burning during the asymptotic giant branch (AGB) phase through the oxygen isotopes has been indicated as a key process that is needed to understand the observed O-18/O-16 relative abundance in presolar grains and in stellar atmospheres. This ratio is strongly influenced by the relative strengths of the reactions O-18(p, alpha)N-15 and O-18(p, gamma)F-19 in low-mass AGB stars. While the former channel has been the focus of a large number of measurements, the (p, gamma) reaction path has only recently received some attention and its stellar reaction rate over a wide temperature range rests on only one measurement. Purpose: Our aim is the direct measurement of states in F-19 as populated through the reaction O-18(p, gamma)F-19 to better determine their influence on the astrophysical reaction rate, and more generally to improve the understanding of the nuclear structure of F-19. Method: Branchings and resonance strengths were measured in the proton energy range E-p(lab) = 150-400 keV, using a high-purity germanium detector inside a massive lead shield. The measurement took place in the ultralow-background environment of the Laboratory for Underground Nuclear Astrophysics (LUNA) experiment at the Gran Sasso National Laboratory, leading to a highly increased sensitivity. Results: The uncertainty of the gamma branchings and strengths was improved for all four resonances in the studied energy range; many new transitions were observed in the case of the 334 keV resonance, and individual gamma decays of the 215 keV resonance were measured for the first time. In addition a number of transitions to intermediate states that decay through alpha emission were identified. The strengths of the observed resonances are generally in agreement with literature values. Conclusions: Our measurements substantially confirm previous determinations of the relevant resonance strengths. Therefore the O-18(p, gamma)F-19 reaction rate does not change with respect to the reaction rate reported in the compilations commonly adopted in the extant computations of red-giant branch and AGB stellar models. Nevertheless, our measurements definitely exclude a nonstandard scenario for the fluorine nucleosynthesis and a nuclear physics solution for the O-18 depletion observed in Group 2 oxygen-rich stardust grains.
Settore FIS/04 - Fisica Nucleare e Subnucleare
Settore FIS/05 - Astronomia e Astrofisica
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/2434/861602
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