Underground study of the $^{17}O(p,\ensuremath{\gamma})^{18}F$ reaction relevant for explosive hydrogen burning

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Underground study of the ${}^{17}O (p, γ) {}^{18}F$ reaction relevant for explosive hydrogen burning

A. Di Leva et al. (LUNA Collaboration)

Phys. Rev. C 89, 015803 – Published 21 January 2014; Erratum Phys. Rev. C 90, 019902 (2014)

Abstract

Background: The ${}^{17}O (p, γ) {}^{18}F$ reaction affects the production of key isotopes (e.g., ${}^{18}F$ and ${}^{18}O$ ) in the explosive hydrogen burning that powers classical novae. Under these explosive conditions, the reaction rate is dominated by contributions from a narrow resonance at $E_{c . m .} = 183 keV$ and by the combined contributions of direct capture and low-energy tails of broad resonances. At present, the astrophysical reaction rate is not well constrained because of the lack of data in the energy region appropriate to classical novae.

Purpose: This study aims at the measurement of the ${}^{17}O$ $(p, γ) {}^{18}F$ reaction cross section in order to determine its reaction rate in the temperature region appropriate to explosive hydrogen burning in novae.

Method: The ${}^{17}O$ $(p, γ) {}^{18}F$ reaction cross section was measured using both the prompt detection of the emitted $γ$ rays and an activation technique. Measurements were carried out at the Laboratory for Underground Nuclear Astrophysics (Gran Sasso, Italy) where the strongly reduced cosmic-ray-induced background allows for improved sensitivity compared to previous studies.

Results: The ${}^{17}O$ $(p, γ) {}^{18}F$ reaction cross section was measured in the range $E_{c . m .} = 160$ to $370 keV$ . The strength of the $E_{c . m .} = 183 keV$ resonance, $ω γ = 1.67 \pm 0.12 μ eV$ , was determined with unprecedented precision. The total $S$ factor was obtained through a combined fit of prompt $γ$ -ray and activation results. An overall global fit including other existing data sets was also carried out and a recommended astrophysical reaction rate is presented.

Conclusions: The reaction rate uncertainty attained in this work is now below the required precision for nova models. We verified, following a full set of hydrodynamic nova models, that the abundances of oxygen and fluorine isotopes obtained with the present reaction rate are determined with 10% precision and put firmer constraints on observational signatures of novae events.