Direct measurement of the astrophysical 19F(p, alpha gamma) 16O reaction in a deep-underground laboratory

Fluorine is one of the most interesting elements in nuclear astrophysics. The 19F(p, alpha)16O reaction is of astrophysical importance in addressing fluorine abundances in the universe and CNO material loss in the first generation stars. As a day-1 campaign in the Jinping Underground Nuclear Astrophysics experiment facility (JUNA), we report the full direct measurement results of the 19F(p, alpha gamma )16O reaction, which is one of the important channels in the 19F(p, alpha)16O reaction. The gamma-ray yields were measured over a center-of-mass energy range of Ec.m. = 72.4-344 keV, covering the astrophysical Gamow window. The measurement has reached down to an unprecedentedly low energy of 72.4 keV. The experiment was performed under the extremely low cosmic -ray-induced background environment of the China JinPing underground Laboratory (CJPL), one of the deepest underground laboratories in the world (2400 m). The astrophysical S factors in the energy region of 72.4-188.8 keV have been derived experimentally for the first time. The present low-energy astrophysical S factors deviate significantly from previous theoretical predictions, and the associated uncertainties are remarkably reduced. The thermonuclear 19F(p, alpha gamma)16O rate has been determined down to a low temperature of approximate to 0.05 GK, for astrophysical modeling, based on a firmer experimental basis. Furthermore, the present work shows that the contribution owing to the (p, alpha 0) channel dominates the total (p, alpha) rate over the entire low temperature region below 0.12 GK, clarifying the role these two channels contributing to the total rate.