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

Abstract

The ${}^{20}\mathrm{Ne}(\mathrm{p},{\hat{\mathrm{I}}}^3{)}^{21}\mathrm{Na}$ 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 $E{}_{\mathrm{cm}}=352$~keV, and of the contribution from the $E_{cm}^{}=368$~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 ${\hat{I}}^3$ rays from the reaction were detected with two high-purity germanium detectors. We obtain a resonance strength $\ddot{I}‰{\hat{I}}^3=(0.112\pm 0.002_{\mathrm{stat}}\pm 0.005_{\mathrm{sys}})$~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 $T\ge 0.1$~GK. Initial astrophysical implications are presented.

8 pages, 4 figures, accepted to PRC (letter)