Measurement of the inelastic branch of the ${}^{14}\mathrm{O}$$(\alpha ,p)$${}^{17}\mathrm{F}$ reaction: Implications for explosive burning in novae and x-ray bursters

A measurement of the inelastic component of the key astrophysical resonance in the ${}^{14}\mathrm{O}$$(\alpha ,p)$${}^{17}\mathrm{F}$ reaction for burning and breakout from hot carbon-nitrogen-oxygen (CNO) cycles is reported. The inelastic component is found to be comparable to the ground-state branch and will enhance the ${}^{14}\mathrm{O}$$(\alpha ,p)$${}^{17}\mathrm{F}$ reaction rate. The current results for the reaction rate confirm that the ${}^{14}\mathrm{O}$$(\alpha ,p)$${}^{17}\mathrm{F}$ reaction is unlikely to contribute substantially to burning and breakout from the CNO cycles under novae conditions. The reaction can, however, contribute strongly to the breakout from the hot CNO cycles under the more extreme conditions found in x-ray bursters.

Figure 1

(a) Center-of-mass energy spectrum for elastically scattered protons produced in the range ${\theta }_{\mathrm{c}.\mathrm{m}.}={131.4}^{°}\text{−}{149.5}^{°}$ by bombarding a thick $({\mathrm{CH}}_2){}_n$ target with $44.2\hspace{0.5em}\mathrm{MeV}\hspace{0.5em}{}^{17}$F ions. The curved line represents an $R$-matrix fit to the data, with the strong known resonance, corresponding to a $5.10\hspace{0.5em}\mathrm{MeV}\hspace{0.5em}{2}^{+}$ state in ${}^{18}\mathrm{Ne}$, being clearly visible. (b) Center-of-mass energy spectrum for inelastically scattered protons measured over the full measured angular range. These events correspond to protons in coincidence with 495 keV deexcitation $\gamma$ rays from the peak shown in Fig. 2.

Figure 2

$\gamma$-ray energy spectrum for events measured by the Miniball array in coincidence with protons in the CD detector system. The most intense peak corresponds to random proton scattering coincidences with annihilation radiation from the ${\beta }^{+}$ decay of the radioactive ${}^{17}\mathrm{F}$ beam in the chamber. The other arrowed peak shows the deexcitation peak from the 495 keV first excited state in ${}^{17}\mathrm{F}$.

Figure 3

Resonant contributions to the ${}^{14}\mathrm{O}$$(\alpha ,p)$${}^{17}\mathrm{F}$ reaction rate incorporating the latest results from the present paper. For resonances above the 6.15 MeV state, resonance parameter values were taken from Ref. [8].