Measurement of the O-18(alpha, gamma )Ne-22 Reaction Rate at JUNA and Its Impact on Probing the Origin of SiC Grains

The O-18(alpha, gamma )Ne-22 reaction is critical for AGB star nucleosynthesis due to its connection to the abundances of several key isotopes, such as Ne-21 and Ne-22. However, the ambiguous resonance energy and spin-parity of the dominant 470 keV resonance leads to substantial uncertainty in the O-18(alpha, gamma )Ne-22 reaction rate for the temperature of interest. We have measured the resonance energies and strengths of the low -energy resonances in O-18(alpha, gamma )(22)2Ne at the Jinping Underground Nuclear Astrophysics experimental facility (JUNA) with improved precision. The key 470 keV resonance energy has been measured to be E-alpha = 474.0 +/- 1.1 keV, with such high precision achieved for the first time. The spin-parity of this resonance state is determined to be 1-, removing discrepancies in the resonance strengths in earlier studies. The results significantly improve the precision of the O-18(alpha, gamma )Ne-22 reaction rates by up to about 10 times compared with the previous data at typical AGB temperatures of 0.1-0.3 GK. We demonstrate that such improvement leads to precise Ne-21 abundance predictions, with an impact on probing the origin of meteoritic stardust SiC grains from AGB stars.