First measurement of the low-energy direct capture in Ne20(p,γ)Na21 and improved energy and strength of the Ec.m.=368keV resonance

The 20 Ne ( p , γ ) 21 Na 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 E c . m . = 352 keV, and of the contribution from the E c . 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 ω γ = ( 0.112 ± 0 . 002 stat ± 0 . 005 sys ) 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.