Alpha-cluster resonances in $^{23}$Na near $^{19}$F+$\alpha$ threshold.

Abundance of $^{19}$F in AGB stars is enhanced by a factor of 2-30 with respect to the solar abundance [1]. This observation provides strong evidence that $^{19}$F is produced in the interior of AGB stars. It was shown in [2] that the final abundance of $^{19}$F depends strongly on the $^{19}$F($\alpha$,p) reaction rate. No experimental data is available for the $^{19}$F($\alpha$,p) reaction cross section below $E_{\alpha}$ = 1.3 MeV. Extrapolation of the $^{19}$F($\alpha$,p) cross section down to the relevant energy range is uncertain due to the unknown properties of relevant resonances in $^{23}$Na. It is the main goal of this work to identify resonances in $^{23}$Na, which may be important for the $^{19}$F($\alpha$,p) reaction. Resonances in $^{23}$Na were populated with a $^{19}$F($^6$Li,d)$^{23}$Na reaction, using a 23 MeV $^6$Li beam. Deuterons were detected at forward angles in coincidence with protons from the proton decay of $^{23}$Na resonances. Angular correlation between deuterons and protons allows for spin-parity assignments for the populated resonances while the magnitude of the $^{19}$F($^6$Li,d) cross section gives information regarding the $\alpha$ spectroscopic factor of the $^{23}$Na. [1] A. Jorissen, et al., A\&A, 261 (1992) 164. [2] M. Lugaro, et al., ApJ, 615 (2004) 934.