Measurement of the 20 and 90 keV Resonances in the ${}^{18}\mathrm{O}(p,\alpha ){}^{15}\mathrm{N}$ Reaction via the Trojan Horse Method

The ${}^{18}\mathrm{O}(p,\alpha ){}^{15}\mathrm{N}$ reaction is of primary importance in several astrophysical scenarios, including fluorine nucleosynthesis inside asymptotic giant branch stars as well as oxygen and nitrogen isotopic ratios in meteorite grains. Thus the indirect measurement of the low energy region of the ${}^{18}\mathrm{O}(p,\alpha ){}^{15}\mathrm{N}$ reaction has been performed to reduce the nuclear uncertainty on theoretical predictions. In particular the strength of the 20 and 90 keV resonances has been deduced and the change in the reaction rate evaluated.

Figure 1

Experimental angular distributions for the ${}^{18}\mathrm{O}(p,\alpha ){}^{15}\mathrm{N}$ reaction for the three resonances in the 0–250 keV energy range. The full lines come from the fitting with the curve of Eq. (1).

Figure 2

Cross section of the TH reaction (full circles). (1), (2), and (3) refer to the 8.014, 8.084, and 8.138 MeV ${}^{19}\mathrm{F}$ levels. The full line represent the result of a fit including three Gaussian curves and a 1st order polynomial.

Figure 3

Ratio of the THM reaction rate (full black line) to the NACRE one [9]. For comparison, the NACRE rate is shown as a red line. The dot-dashed and dotted lines show the upper and lower limits allowed by experimental uncertainties.