First measurement of the low-energy direct capture in 20Ne(p, γ) 21Na and improved energy and strength of the Ec.m. = 368 keV resonance

The 20Ne(p, γ ) 21Na reaction is the slowest in the NeNa cycle and directly affects the abundances of the Ne and Na isotopes in a variety of astrophysical sites. Here we report the measurement of its direct capture contribution, for the first time below Ec.m. = 352 keV, and of the contribution from the Ec.m. = 368 keV resonance, which dominates the reaction rate at T = 0.03–1.00 GK. The experiment was performed deep underground at the Laboratory for Underground Nuclear Astrophysics, using a high-intensity proton beam and a windowless neon gas target. Prompt γ rays from the reaction were detected with two high-purity germanium detectors. We obtain a resonance strength ωγ = (0.112 ± 0.002stat ± 0.005sys) meV, with an uncertainty a factor of 3 smaller than previous values. Our revised reaction rate is 20% lower than previously adopted at T < 0.1 GK and agrees with previous estimates at temperatures T 0.1 GK. Initial astrophysical implications are presented.