Nuclear reactions have been crucial in the evolution of the universe since the big bang. The cross section of nuclear reaction that occurs during the early evolution of the star is extremely low, so it cannot be accurately measured in a ground laboratory. The China Jinping Underground Laboratory (CJPL), which is the deepest operational underground laboratory in the world, offers unique ultra-low background conditions that facilitate the direct evaluation of the nuclear reactions occurring during the early evolution of stars.

Asymptotic giant branch (AGB) stars are thought to be the major contributor to Galactic fluorine production. However, the astronomical fluorine overabundance cannot be explained by using the current standard AGB models. Direct measurements of ¹⁹F(p,αγ)¹⁶O reactions can help solve this problem.

Experiments were conducted on a high-current 400-kV JUNA (Jinping Underground laboratory for Nuclear Astrophysics) accelerator at the CJPL. A 4π BGO detector array was specially designed for the JUNA project.

The astrophysical S factors in the energy region of 72.4~188.8 keV were experimentally derived for the first time, covering the astrophysical Gamow window. The thermonuclear ¹⁹F(p,αγ)¹⁶O rate was determined at a low temperature of about 0.05 GK for astrophysical modeling. The present low-energy S factors significantly deviated from previous theoretical predictions, and the associated uncertainties were considerably reduced.